Comprehensive Income - Components of Other Comprehensive Income (Loss) and Related Tax Effects (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Equity [Abstract]
Unrealized holding gains (losses) on available for sale securities before reclassifications	$ (29,561)	$ 12,710
Tax effect	8,739	(3,758)
Unrealized holding gains (losses) on available for sale securities, net of tax	(20,822)	8,952
Change in unfunded status of the supplemental retirement plans before reclassifications	448	(89)
Amounts reclassified out of accumulated other comprehensive income (loss):
Amortization of prior service cost	(14)	(13)
Amortization of actuarial losses	478	102
Total amounts reclassified out of accumulated other comprehensive income (loss)	464	89
Change in unfunded status of the supplemental retirement plans after reclassifications	912	0
Tax effect	0	0
Change in unfunded status of the supplemental retirement plans, net of tax	912	0
Other comprehensive income (loss)	$ (19,910)	$ 8,952

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