Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (loss) Pre-Tax and After-Tax (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Net unrealized gains (losses) on investments available for sale arising during the period, Pre-tax	$ 1,207	$ (694)	$ 9,248	$ 10,460
Less: Amounts reclassified from accumulated other comprehensive income (loss), Pre-tax	(803)	(101)	(2,450)	(1,344)
Net current period other comprehensive income (loss), Pre-tax	404	(795)	6,798	9,116
Net unrealized gains (losses) on investments available for sale arising during the period, Tax	461	(265)	3,535	3,998
Less: Amounts reclassified from accumulated other comprehensive income (loss), Tax	(308)	(39)	(938)	(513)
Net current period other comprehensive income (loss), Tax	153	(304)	2,597	3,485
Net unrealized gains (losses) on investments available for sale arising during the period, After-tax	746	(429)	5,713	6,462
Less: Amounts reclassified from accumulated other comprehensive income (loss), After-tax	(495)	(62)	(1,512)	(831)
Net current period other comprehensive income (loss), After-tax	$ 251	$ (491)	$ 4,201	$ 5,631

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

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Amount before 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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