Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 9,142	$ 21,930
Available-for-sale investments:
Change in net unrealized loss on investments, net of tax	(407)	(62)
Less: reclassification adjustment for net realized gain (loss) included in net income, net of tax	16	(8)
Other comprehensive loss, net of tax	(391)	(70)
Comprehensive income	$ 8,751	$ 21,860

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

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