Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (loss) Pre-Tax and After-Tax (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
After-tax:
Other comprehensive income (loss)	$ (8,946)	$ 11,984
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
OCI, Pre-tax:
Pre-tax, Unrealized holding gains (losses) arising during the period	(11,226)	16,045
Pre-tax, Less: Reclassification adjustments (gains) losses realized in net income	(299)	(145)
Pre-tax, Other comprehensive income (loss)	(11,525)	15,900
OCI, Tax:
Tax, Unrealized holding gains (losses) arising during the period	(2,505)	3,953
Income taxes	(74)	(37)
Tax, Other comprehensive income (loss)	(2,579)	3,916
After-tax:
After-tax, Unrealized holding gains (losses) arising during the period	(8,721)	12,092
After-tax, Less: Reclassification adjustments (gains) losses realized in net income	(225)	(108)
Other comprehensive income (loss)	(8,946)	$ 11,984
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] \| Cumulative Effect, Period Of Adoption, Adjustment [Member]
OCI, Pre-tax:
Pre-tax, Less: Reclassification adjustments (gains) losses realized in net income	791
OCI, Tax:
Income taxes	194
After-tax:
After-tax, Less: Reclassification adjustments (gains) losses realized in net income	597
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] \| Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
OCI, Pre-tax:
Pre-tax, Other comprehensive income (loss)	(10,734)
OCI, Tax:
Tax, Other comprehensive income (loss)	(2,385)
After-tax:
Other comprehensive income (loss)	$ (8,349)

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