Investments (Balance of and Changes in AOCI Components) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, Beginning of Period			$ 64,805
Income tax benefit (expense)	$ 38,202	$ 21,784	74,946	$ (12,681)
Balance, End of Period	249,787		249,787		$ 64,805
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, Beginning of Period			(397)	(67)	(67)
Change in OCI before reclassifications			153	(391)
Amounts reclassified from AOCI			0	0
Income tax benefit (expense)			(54)	137
Balance, End of Period	(298)	(321)	(298)	(321)	(397)	$ (67)
Total net unrealized investment gains (losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, Beginning of Period			65,202	178,758	178,758
Change in OCI before reclassifications			356,594	(97,212)
Amounts reclassified from AOCI	1,517	(5,071)	(72,160)	(9,115)
Income tax benefit (expense)			(99,551)	37,214
Balance, End of Period	250,085	109,645	250,085	109,645	65,202	178,758
Cash Flow Hedge Gain (Loss) To AOCI			31,000	40,000	48,000	12,000
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, Beginning of Period			64,805	178,691	178,691
Change in OCI before reclassifications			356,747	(97,603)
Amounts reclassified from AOCI	1,517	(5,071)	(72,160)	(9,115)
Income tax benefit (expense)			(99,605)	37,351
Balance, End of Period	$ 249,787	$ 109,324	$ 249,787	$ 109,324	$ 64,805	$ 178,691