Annual report pursuant to Section 13 and 15(d)

Effective Income Tax Rate Reconciliation (Details)

v3.8.0.1
Effective Income Tax Rate Reconciliation (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Subsequent Event [Line Items]                        
Computed income tax expense at federal rate                   $ 104,215 $ 127,957 $ 166,432
Federal income tax rate applicable to corporations                   35.00% 35.00% 35.00%
State taxes, net of federal benefit, if applicable                   $ 37 $ 106 $ 114
State taxes, net of federal benefit, if applicable, effective tax rate                   0.00% 0.00% 0.00%
Permanent differences in taxable income from GAAP net income                   $ 1,208 $ 401 $ 4,203
Permanent differences in taxable income from GAAP net income, effective tax rate                   0.00% 0.00% 1.00%
Dividends paid deduction                   $ (115,942) $ (116,150) $ (187,309)
Dividends paid deduction, effective tax rate                   (39.00%) (32.00%) (39.00%)
(Benefit from) provision for income taxes $ 10,618 $ (5,342) $ 8,759 $ (24,517) $ 38,443 $ (16,825) $ (14,761) $ 5,458   $ (10,482) $ 12,314 $ (16,560)
(Benefit from) provision for income taxes, effective tax rate                   (4.00%) 3.00% (3.00%)
Tax provision related to the decrease in the federal income tax rate applicable to corporations                   $ 17,500    
Subsequent Event [Member]                        
Subsequent Event [Line Items]                        
Federal income tax rate applicable to corporations                 21.00%