Annual report pursuant to Section 13 and 15(d)

Income Taxes - Common Stock Distribution (Details)

v3.6.0.2
Income Taxes - Common Stock Distribution (Details) - $ / shares
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) $ 3 $ 2.75 $ 2.57
Dividend Declared [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 3 2.75 2.57
Preferred Stock, Dividends declared per share (in dollars per share) 1.8436 1.5569  
Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 1.182 1.98 1.908
Preferred Stock, Dividends declared per share (in dollars per share) 1.8436 1.5569  
Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0.0534 0.924
Preferred Stock, Dividends declared per share (in dollars per share) 0 0.0419  
Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0 0
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 1.818 0.77 0.662
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment One [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.75 0.65 0.625
Preferred Stock, Dividends declared per share (in dollars per share) 0.4609 0.6351  
Installment One [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.2955 0.468 0.464
Preferred Stock, Dividends declared per share (in dollars per share) 0.4609 0.6351  
Installment One [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0.0126 0.225
Preferred Stock, Dividends declared per share (in dollars per share) 0 0.0171  
Installment One [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0 0
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment One [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.4545 0.1820 0.161
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment Two [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.75 0.675 0.645
Preferred Stock, Dividends declared per share (in dollars per share) 0.4609 0.4609  
Installment Two [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.2955 0.486 0.479
Preferred Stock, Dividends declared per share (in dollars per share) 0.4609 0.4609  
Installment Two [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0.0131 0.232
Preferred Stock, Dividends declared per share (in dollars per share) 0 0.0124  
Installment Two [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0 0
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment Two [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.4545 0.1890 0.166
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment Three [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.75 0.675 0.65
Preferred Stock, Dividends declared per share (in dollars per share) 0.46091 0.4609  
Installment Three [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.2955 0.486 0.4825
Preferred Stock, Dividends declared per share (in dollars per share) 0.46091 0.4609  
Installment Three [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0.0131 0.2335
Preferred Stock, Dividends declared per share (in dollars per share) 0 0.0124  
Installment Three [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0 0
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment Three [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.4545 0.1890 0.1675
Preferred Stock, Dividends declared per share (in dollars per share) 0 0  
Installment Four [Member] | Dividend Declared [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.75 0.75 0.65
Preferred Stock, Dividends declared per share (in dollars per share) 0.4609    
Installment Four [Member] | Ordinary Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.2955 0.54 0.4825
Preferred Stock, Dividends declared per share (in dollars per share) 0.4609    
Installment Four [Member] | Qualified Dividends [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0.0146 0.2335
Preferred Stock, Dividends declared per share (in dollars per share) 0    
Installment Four [Member] | Capital Gain Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0 0 0
Preferred Stock, Dividends declared per share (in dollars per share) 0    
Installment Four [Member] | Nondividend Distribution [Member]      
Dividends Payable [Line Items]      
Common Stock, Dividends declared per share (in dollars per share) 0.4545 $ 0.21 $ 0.1675
Preferred Stock, Dividends declared per share (in dollars per share) $ 0    
Common Stock [Member]      
Dividends Payable [Line Items]      
Ordinary income dividend percentage 39.40%    
Return of capital percentage 60.60%    
Qualified dividend income percentage 0.00%    
Preferred Stock [Member]      
Dividends Payable [Line Items]      
Ordinary income dividend percentage 100.00%    
Return of capital percentage 0.00%    
Qualified dividend income percentage 0.00%