Change in Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 820,920
Other comprehensive income (loss) before reclassifications	39,563	$ (6,723)	$ 2,889
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(668)	(519)	(1,764)
Net current-period other comprehensive income (loss)	38,895	(7,242)	1,125
Less: Reclassification due to the adoption of ASU No. 2018-02			(1,660)
Ending Balance	1,850,306	820,920
Net change in investment securities available for sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(14,553)	(7,842)	(8,194)
Other comprehensive income (loss) before reclassifications	41,733	(6,695)	3,073
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(253)	(16)	(1,280)
Net current-period other comprehensive income (loss)	41,480	(6,711)	1,793
Less: Reclassification due to the adoption of ASU No. 2018-02			(1,441)
Ending Balance	26,927	(14,553)	(7,842)
Net change in investment securities held to maturity
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	779	1,223	1,392
Other comprehensive income (loss) before reclassifications	(2)	6	0
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(309)	(450)	(394)
Net current-period other comprehensive income (loss)	(311)	(444)	(394)
Less: Reclassification due to the adoption of ASU No. 2018-02			225
Ending Balance	468	779	1,223
Net change in defined benefit plan
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	834	865	957
Other comprehensive income (loss) before reclassifications	(4,045)	22	0
Less: Amounts reclassified from accumulated other comprehensive income (loss)	(106)	(53)	(90)
Net current-period other comprehensive income (loss)	(4,151)	(31)	(90)
Less: Reclassification due to the adoption of ASU No. 2018-02			(2)
Ending Balance	(3,317)	834	865
Net change in fair value of derivatives used for cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(2,454)	(2,398)	(1,772)
Other comprehensive income (loss) before reclassifications		(56)	(184)
Less: Amounts reclassified from accumulated other comprehensive income (loss)		0	0
Net current-period other comprehensive income (loss)		(56)	(184)
Less: Reclassification due to the adoption of ASU No. 2018-02			(442)
Ending Balance		(2,454)	(2,398)
Net change in fair value of derivatives used for cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	1,877
Less: Amounts reclassified from accumulated other comprehensive income (loss)	0
Net current-period other comprehensive income (loss)	1,877
Ending Balance	(577)
Accumulated Other Comprehensive (Loss) Income
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(15,394)	(8,152)	(7,617)
Ending Balance	$ 23,501	$ (15,394)	$ (8,152)

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings

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