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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, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
After-tax
Other comprehensive income (loss)	$ 7,996	$ (16,910)	$ 26,068	$ (8,946)	$ (8,914)	$ 17,122
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
Pre-tax
Unrealized holding gains arising during the period	10,264		34,661		(12,161)	23,435
Less: Reclassification adjustments for (gains) losses realized in net income	245		(168)		447	(467)
Other comprehensive income (loss)	10,509		34,493		(11,714)	22,968
Tax
Unrealized holding gains arising during the period	2,454		8,466		(2,907)	5,961
Income taxes	59		(41)		107	(115)
Other comprehensive income (loss)	2,513		8,425		(2,800)	5,846
After-tax
Unrealized holding gains arising during the period	7,810		26,195		(9,254)	17,474
Less: Reclassification adjustments for (gains) losses realized in net income	186		(127)		340	(352)
Other comprehensive income (loss)	$ 7,996		$ 26,068		(8,914)	17,122
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent \| Cumulative effect of change in accounting principle (ASU 2016-13)
Pre-tax
Other comprehensive income (loss)					0	791
Tax
Other comprehensive income (loss)					0	194
After-tax
Other comprehensive income (loss)					0	597
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent \| Change in accumulated other comprehensive income
Pre-tax
Other comprehensive income (loss)					(11,714)	23,759
Tax
Other comprehensive income (loss)					(2,800)	6,040
After-tax
Other comprehensive income (loss)					$ (8,914)	$ 17,719