Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (loss) Pre-Tax and After-Tax (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
After-tax:
Other comprehensive income (loss)	$ 11,955	$ 11,984	$ (1,849)	$ (4,050)	$ 23,939	$ (5,899)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
OCI, Pre-tax:
Pre-tax, Unrealized holding gains (losses) arising during the period	15,825		(2,488)		31,870	(10,522)
Pre-tax, Less: Reclassification adjustments (gains) losses realized in net income	36		32		(109)	2,797
Pre-tax, Other comprehensive income (loss)	15,861		(2,456)		31,761	(7,725)
OCI, Tax:
Tax, Unrealized holding gains (losses) arising during the period	3,896		(618)		7,849	(2,507)
Tax, Less: Reclassification adjustments (gains) losses realized in net income	10		11		(27)	681
Tax, Other comprehensive income (loss)	3,906		(607)		7,822	(1,826)
After-tax:
After-tax, Unrealized holding gains (losses) arising during the period	11,929		(1,870)		24,021	(8,015)
After-tax, Less: Reclassification adjustments (gains) losses realized in net income	26		21		(82)	2,116
Other comprehensive income (loss)	$ 11,955		$ (1,849)		$ 23,939	$ (5,899)

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