Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities losses, net	$ 0	$ (267)
Investment securities interest revenue	136,547	136,516
Deposit interest expense	(15,075)	(15,957)
Salaries and employee benefits expense	(51,358)	(47,503)
Other expense	(4,022)	(3,684)
Total before tax	40,691	57,218
Income tax (expense) benefit	(8,807)	(12,956)
Net income	31,884	44,262
Reclassifications Out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(223)	(469)
Reclassifications Out of Accumulated Other Comprehensive Income | Realized gains (losses) on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Securities losses, net	0	(267)
Income tax (expense) benefit	0	68
Net income	0	(199)
Reclassifications Out of Accumulated Other Comprehensive Income | Amortization of losses included in net income on available-for-sale securities transferred to held to maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities interest revenue	(83)	(84)
Income tax (expense) benefit	20	20
Net income	(63)	(64)
Reclassifications Out of Accumulated Other Comprehensive Income | Amortization of losses included in net income on derivative financial instruments accounted for as cash flow hedges:
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Deposit interest expense	0	(102)
Income tax (expense) benefit	0	26
Net income	0	(76)
Reclassifications Out of Accumulated Other Comprehensive Income | Prior service cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits expense	(133)	(159)
Reclassifications Out of Accumulated Other Comprehensive Income | Actuarial losses
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other expense	(81)	(15)
Reclassifications Out of Accumulated Other Comprehensive Income | Reclassifications related to defined benefit pension plan activity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(214)	(174)
Income tax (expense) benefit	54	44
Net income	$ (160)	$ (130)