Fair Value Measurements - Recurring basis Level 3 rollforward (Details) - Recurring basis - Level 3 - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fixed maturities available-for-sale, Corporate debt securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	$ 9,738	$ 11,639
Net income (loss)	0	0
Other comprehensive income (loss)	(13)	(364)
Settlements	(438)	(344)
Balance at the end of the period	9,287	10,931
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
Embedded derivatives - GLWB
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	11,095	5,712
Net income (loss)	7,102	1,670
Other comprehensive income (loss)	0	0
Settlements	0	0
Balance at the end of the period	3,993	4,042
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets and liabilities	$ 7,102	$ 1,670