Fair Value Measurements - Recurring basis Level 3 rollforward (Details) - Recurring basis - Level 3 - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fixed maturities available-for-sale, Corporate debt securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	$ 9,287	$ 10,931	$ 9,738	$ 11,639
Net income (loss)	0	0	0	0
Other comprehensive income (loss)	129	84	116	(280)
Settlements	(446)	(312)	(884)	(656)
Balance at the end of the period	8,970	10,703	8,970	10,703
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets and liabilities	0	0	0	0
Embedded derivatives - GLWB
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	3,993	4,042	11,095	5,712
Net income (loss)	3,480	(5,553)	10,582	(3,883)
Other comprehensive income (loss)	0	0	0	0
Settlements	0	0	0	0
Balance at the end of the period	513	9,595	513	9,595
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets and liabilities	$ 3,480	$ (5,553)	$ 10,582	$ (3,883)