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Accumulated Other Comprehensive Income (Loss) - Reclassifications (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on sales of available for sale securities									$ 11,895	$ 4,415	$ 4,269
Income tax expense	$ (7,641)	$ (5,621)	$ (4,623)	$ (3,490)	$ (8,298)	$ (6,337)	$ (7,749)	$ (6,941)	(21,375)	(29,325)	(28,999)
Subordinated debentures and term loans									6,944	8,309	8,233
Salaries and employee benefits									155,937	144,037	131,704
Total reclassifications for the period, net of tax									8,615	3,140	3,018
Unrealized gains (losses) on available for sale securities
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period, net of tax									9,397	3,488	3,373
Unrealized gains (losses) on cash flow hedges
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period, net of tax									(716)	(264)	(371)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) \| Unrealized gains (losses) on available for sale securities
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on sales of available for sale securities									11,895	4,415	4,269
Income tax expense									(2,498)	(927)	(896)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) \| Unrealized gains (losses) on cash flow hedges
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense									190	70	99
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) \| Unrealized gains (losses) on cash flow hedges \| Interest rate contracts
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Subordinated debentures and term loans									(906)	(334)	(470)
Amount Reclassified from Accumulated Other Comprehensive Income (Loss) \| Unrealized gains (losses) on defined benefit plans
Reclassification Adjustments out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense									18	22	(4)
Salaries and employee benefits									(84)	(106)	20
Total reclassifications for the period, net of tax									$ (66)	$ (84)	$ 16