Changes in Accumulated Other Comprehensive Income by Component - Summary of Changes in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016
Accumulated other comprehensive income
Beginning balance	$ 338,842
Other comprehensive income before reclassifications	1,162	$ 909
Losses (gains) reclassified from other comprehensive income	1	(144)
Net current period change in other comprehensive income	1,163	765
Ending balance	390,456
Available-for-sale securities, tax	600	400
Accumulated Other Comprehensive Income (Loss), net of taxes
Accumulated other comprehensive income
Beginning balance	(319)	543
Ending balance	$ 844	$ 1,308

Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount of tax expense (benefit), after 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 other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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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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