Other Comprehensive Income (Loss) - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2014
Equity [Abstract]
Reclassification of net gains or (losses) included in other comprehensive income	$ 0	$ 236	$ 233	$ 566
Effect of disproportionate tax on accumulated other comprehensive income (loss)					$ (16,600)

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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