Accumulated Other Comprehensive Income (Loss) - Summary of Changes (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 1,875,645	$ 1,786,437
Other comprehensive income (loss) before reclassifications	(12,349)	41,756
Amounts reclassified from accumulated other comprehensive income	(2,407)	(5,785)
Total other comprehensive income (loss), net of tax	(14,756)	35,971
Ending balance	1,871,800	1,809,095
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	74,836	27,874
Ending balance	60,080	63,845
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Beginning balance	87,988	38,872
Other comprehensive income (loss) before reclassifications	(12,382)	42,909
Amounts reclassified from accumulated other comprehensive income	(2,812)	(6,067)
Total other comprehensive income (loss), net of tax	(15,194)	36,842
Ending balance	72,794	75,714
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(1,594)	(1,141)
Other comprehensive income (loss) before reclassifications	33	(1,153)
Amounts reclassified from accumulated other comprehensive income	405	282
Total other comprehensive income (loss), net of tax	438	(871)
Ending balance	(1,156)	(2,012)
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(11,558)	(9,857)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	0
Total other comprehensive income (loss), net of tax	0	0
Ending balance	$ (11,558)	$ (9,857)