Investments - Reconciliation of Net Unrealized Investment Gains (Losses) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 1,290,550
Change in net unrealized investment gains (losses) on securities	$ (7,762)	$ (52,444)	106,136	$ (159,540)
Cumulative effect of change in accounting principle	0	0	0	(15,041)
Ending balance	1,499,677	1,350,441	1,499,677	1,350,441
Net Unrealized Investment Gains (Losses) on Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	210,839	178,040	96,941	300,177
Cumulative effect of change in accounting principle				(15,041)
Ending balance	203,077	125,596	203,077	125,596
Net Unrealized Investment Gains (Losses) on Securities [Member] \| Fixed maturity securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	245,319	206,293	111,712	286,176
Change in net unrealized investment gains (losses) on securities	100,693	(61,724)	240,705	(129,009)
Reclassification of net investment (gains) losses on securities to net income	(114,925)	429	(121,330)	2,872
Ending balance	$ 231,087	$ 144,998	$ 231,087	$ 144,998

Other Comprehensive (Income) Loss, Reclassification Adjustment From AOCI For New Accounting Pronouncements, Net Of Tax

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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