Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2007	Dec. 31, 2015
Valuation Allowance [Line Items]
Number of years used in the cumulative income position calculation	3 years
Provision for income tax	$ 34,497	$ 47,883
Change in valuation allowance	0	(44,498)
Provision for income taxes	34,497	3,385
Net operating loss carryforwards, regular tax basis	1,900,000
Net operating loss carryforwards for computing the alternative minimum tax	1,000,000
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	187,400
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	49,300
Total amount of unrecognized tax benefits	107,400
Total amount of the unrecognized tax benefits that would affect our effective tax rate	94,100
Unrecognized tax benefits, accrued interest	$ 28,100			$ 27,800
Other Comprehensive Income (Loss)
Valuation Allowance [Line Items]
Change in valuation allowance		$ (6,500)