Accumulated Other Comprehensive Income (Loss) - Summary of Changes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 1,912,571	$ 1,875,645
Other comprehensive income (loss) before reclassifications	(139,248)	(37,804)
Amounts reclassified from accumulated other comprehensive income	(257)	(1,222)
Total other comprehensive income (loss), net of tax	(139,505)	(39,026)
Ending balance	1,807,633	1,805,856
Total
Accumulated Other Comprehensive Income (Loss)
Beginning balance	55,113	74,836
Total other comprehensive income (loss), net of tax	(139,505)	(39,026)
Ending balance	(84,392)	35,810
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income (Loss)
Beginning balance	59,774	87,988
Other comprehensive income (loss) before reclassifications	(139,487)	(37,850)
Amounts reclassified from accumulated other comprehensive income	(447)	(1,421)
Total other comprehensive income (loss), net of tax	(139,934)	(39,271)
Ending balance	(80,160)	48,717
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(660)	(1,594)
Other comprehensive income (loss) before reclassifications	239	46
Amounts reclassified from accumulated other comprehensive income	190	199
Total other comprehensive income (loss), net of tax	429	245
Ending balance	(231)	(1,349)
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(4,001)	(11,558)
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	$ (4,001)	$ (11,558)