Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2012
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before tax amount	$ (67,291)	$ (52,065)
Other comprehensive income (loss), tax (expense) benefit
Other comprehensive income (loss), tax (expense) benefit	24,917	(43,411)
Other comprehensive income (loss):
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	(42,374)
Other comprehensive income (loss), net of tax		(95,476)
Deferred tax asset valuation allowance released			$ 63,000
Deferred tax asset valuation allowance reclassified from AOCI		63,000
Unrealized/Recognized Gains (Losses)
Other comprehensive income (loss), before tax amount
Other comprehensive income (loss), before reclassifications, before tax	(2,601)	7,422
Amounts reclassified from accumulated other comprehensive income (loss), before tax	(64,690)	(59,487)
Other comprehensive income (loss), tax (expense) benefit
Other comprehensive income (loss), before reclassifications, tax (expense) benefit	963	(2,744)
Amounts reclassified from accumulated other comprehensive income (loss), tax (expense) benefit	23,954	(40,667)
Other comprehensive income (loss):
Other comprehensive income (loss), before reclassifications, net of tax	(1,638)	4,678
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	$ (40,736)	$ (100,154)