Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net income	$ 166,730	$ 208,949	$ 337,687	$ 323,435
Unrealized gains (losses) on investments:
Unrealized holding gains (losses) arising during the period	72,000	(27,804)	150,023	(88,447)
Less: Reclassification adjustment for net gains (losses) included in net income	1,029	(1,336)	638	(4,468)
Net unrealized gains (losses) on investments	70,971	(26,468)	149,385	(83,979)
Foreign Currency Translation Adjustments
Net foreign currency translation adjustments	(3)	0	(3)	3
Other comprehensive income (loss), net of tax	70,968	(26,468)	149,382	(83,976)
Comprehensive income	$ 237,698	$ 182,481	$ 487,069	$ 239,459

Other Comprehensive Gain (Loss), Unrealized Holding Gains (Losses) on Investments [Abstract]

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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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 and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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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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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

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