Equity (Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 165,346
Income tax benefit (expense)	55,174	$ (43,372)	$ (3,322)
Ending balance	(28,296)	165,346
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(234)	(402)	(397)
Change in OCI before reclassifications	(17,745)	259	(8)
Amounts reclassified from AOCI	0	0	0
Income tax benefit (expense)	581	(91)	3
Ending balance	(17,448)	(234)	(402)
Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	165,580	71,377	65,202
Change in OCI before reclassifications	(257,432)	164,482	74,040
Amounts reclassified from AOCI	(2,549)	(26,998)	(64,540)
Income tax benefit (expense)	54,593	(43,281)	(3,325)
Ending balance	(10,848)	165,580	71,377
Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	165,346	70,975	64,805
Change in OCI before reclassifications	(275,177)	164,741	74,032
Amounts reclassified from AOCI	(2,549)	(26,998)	(64,540)
Income tax benefit (expense)	55,174	(43,372)	(3,322)
Cumulative effect of adoption				$ 30,400
Ending balance	(28,296)	165,346	70,975
Cash flow hedges | Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(18,000)	41,000
Ending balance	22,000	$ (18,000)	$ 41,000
ASU 2016-01 | Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption	0
ASU 2016-01 | Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption	(1,539)
ASU 2016-01 | Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption	(1,539)			(1,539)
ASU 2018-02 | Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption	(50)
ASU 2018-02 | Net Unrealized Investment Gains (Losses)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption	30,499
ASU 2018-02 | Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effect of adoption	$ 30,449			$ 30,449