Fair Value Measurements - Recurring basis Level 3 rollforward (Details) - Recurring basis - Level 3 - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fixed maturities available-for-sale, Corporate debt securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	$ 8,970	$ 10,703	$ 9,738	$ 11,639
Net income (loss)	0	0	0	0
Other comprehensive income (loss)	105	166	221	83
Settlements	(452)	(432)	(1,336)	(1,275)
Transfers out of Level 3		(357)		(367)
Balance at the end of the period	8,623	10,080	8,623	10,080
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	(513)	(9,595)	(11,095)	(5,712)
Net income (loss)	7,362	(626)	17,944	(4,509)
Other comprehensive income (loss)	0	0	0	0
Settlements	0	0	0	0
Transfers out of Level 3		0		0
Balance at the end of the period	6,849	(10,221)	6,849	(10,221)
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets and liabilities	$ 7,362	$ (626)	$ 17,944	$ (4,509)