Fair Value - Recurring basis Level 3 rollforward (Details) - Recurring basis - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Embedded derivatives - GLWB
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period		$ 5,712
Balance at the end of the period		11,095		$ 5,712
Significant unobservable inputs (Level 3)
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period				4,538		$ 5,878
Net income						0
Other comprehensive income (loss)						(178)
Settlements						(1,126)
Transfers out of Level 3	[1]					(36)
Balance at the end of the period						4,538
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets held at December 31, 2016						0
Significant unobservable inputs (Level 3) | Corporate debt securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period		11,639		4,538		5,842
Net income		0		0		0
Other comprehensive income (loss)		169		273		(178)
Settlements		(1,703)		(1,478)		(1,126)
Transfers into Level 3	[2]			11,236
Transfers out of Level 3		(367)	[3]	(2,930)	[2]	0	[1]
Balance at the end of the period		9,738		11,639		4,538
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets held at December 31, 2016		0		0		0
Significant unobservable inputs (Level 3) | Asset-backed securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period				0		36
Net income						0
Other comprehensive income (loss)						0
Settlements						0
Transfers out of Level 3	[1]					(36)
Balance at the end of the period						0
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets held at December 31, 2016						0
Significant unobservable inputs (Level 3) | Embedded derivatives - GLWB
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period		5,712		11,257		0
Net income		5,383		(5,545)		11,257
Other comprehensive income (loss)		0		0		0
Settlements		0		0		0
Transfers into Level 3				0
Transfers out of Level 3		0	[3]	0	[2]	0	[1]
Balance at the end of the period				5,712		11,257
Total gains (losses) for the period included in net income attributable to the change in unrealized gains and losses relating to assets held at December 31, 2016		$ 5,383		$ (5,545)		$ 11,257

[1] Transfers out of Level 3 are due primarily to increased observability of inputs in valuation methodologies as evidenced by corroboration of market prices with multiple pricing vendors and internal models.

[2] Transfers out of Level 3 are due primarily to increased observability of inputs in valuation methodologies as evidenced by corroboration of market prices with multiple pricing vendors and internal models.

[3] Transfers out of Level 3 are due primarily to increased observability of inputs in valuation methodologies as evidenced by corroboration of market prices with multiple pricing vendors and internal models.