Accumulated Other Comprehensive Income (Loss) - Summary of Changes (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 1,408,260	$ 1,303,463	$ 901,657
Other comprehensive income before reclassifications	52,436	(14,870)
Amounts reclassified from accumulated other comprehensive income	(3,140)	(3,018)
Period change	49,296	(17,888)	10,673
Reclassification adjustment under ASU 2018-02		(626)
Ending balance	1,786,437	1,408,260	1,303,463
Total
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(21,422)	(2,908)	(13,581)
Period change	49,296	(17,888)	10,673
Reclassification adjustment under ASU 2018-02		(626)
Ending balance	27,874	(21,422)	(2,908)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(6,343)	8,970
Other comprehensive income before reclassifications	48,703	(13,872)
Amounts reclassified from accumulated other comprehensive income	(3,488)	(3,373)
Period change	45,215	(17,245)
Reclassification adjustment under ASU 2018-02		1,932
Ending balance	38,872	(6,343)	8,970
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(559)	(1,125)
Other comprehensive income before reclassifications	(846)	437
Amounts reclassified from accumulated other comprehensive income	264	371
Period change	(582)	808
Reclassification adjustment under ASU 2018-02		(242)
Ending balance	(1,141)	(559)	(1,125)
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(14,520)	(10,753)
Other comprehensive income before reclassifications	4,579	(1,435)
Amounts reclassified from accumulated other comprehensive income	84	(16)
Period change	4,663	(1,451)
Reclassification adjustment under ASU 2018-02		(2,316)
Ending balance	$ (9,857)	$ (14,520)	$ (10,753)

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

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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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