Investments (Balance of and Changes in AOCI Components) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	$ 64,805
Income tax benefit (expense)	44,095	$ (13,346)
Balance	180,132		$ 64,805
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	(397)	(67)	(67)
Change in OCI before reclassifications	219	(520)
Amounts reclassified from AOCI	0	0
Income tax benefit (expense)	(76)	182
Balance	(254)	(405)	(397)	$ (67)
Total net unrealized investment gains (losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	65,202	178,758	178,758
Change in OCI before reclassifications	162,282	81,731
Amounts reclassified from AOCI	14,924	(2,114)
Income tax benefit (expense)	(62,022)	(27,866)
Balance	180,386	230,509	65,202	178,758
Cash Flow Hedge Gain (Loss) To AOCI	31,000	36,000	48,000	12,000
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance	64,805	178,691	178,691
Change in OCI before reclassifications	162,501	81,211
Amounts reclassified from AOCI	14,924	(2,114)
Income tax benefit (expense)	(62,098)	(27,684)
Balance	$ 180,132	$ 230,104	$ 64,805	$ 178,691