Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2007	Dec. 31, 2015	Dec. 31, 2014
Valuation Allowance [Line Items]
Number of years used in the cumulative income position calculation			3 years
Provision for income tax	$ 56,018	$ 39,991	$ 90,515	$ 87,874
Change in valuation allowance	0	(38,669)	0	(83,167)
Provision for income taxes	56,018	1,322	90,515	4,707
Net operating loss carryforwards, regular tax basis	1,700,000		1,700,000
Net operating loss carryforwards for computing the alternative minimum tax	800,000		800,000
Information regarding income tax examinations [Abstract]
Amount of IRS assessment for unpaid taxes and penalties related to REMIC issue							$ 197,500
Estimate of federal interest that may be due	191,200		191,200
Amount of payment made related to the IRS assessment on the REMIC issue					$ 65,200
Amount of IRS assessment for unpaid taxes and penalties related to disallowance of carryback of 2009 net operating loss							$ 261,400
Estimate of additional state income taxes and interest that may be due	49,700		49,700
Total amount of unrecognized tax benefits	107,600		107,600
Total amount of the unrecognized tax benefits that would affect our effective tax rate	94,200		94,200
Unrecognized tax benefits, accrued interest	$ 28,300		$ 28,300			$ 27,800
Other Comprehensive Income (Loss)
Valuation Allowance [Line Items]
Change in valuation allowance		$ (22,000)		$ (15,600)