Other Comprehensive Loss - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net gain on securities transactions									$ 72	$ 2,221	$ 57
Income tax expense (benefit)	$ (8,026)	$ (9,938)	$ (8,802)	$ (7,689)	$ (6,026)	$ (8,575)	$ (4,568)	$ (6,361)	(34,455)	(25,530)	(46,528)
Net of tax	$ 25,951	$ 31,399	$ 24,393	$ 30,890	$ 35,763	$ 35,468	$ 19,243	$ 27,913	112,633	118,387	93,949
Compensation and employee benefits									116,849	111,496	109,353
Securities available for sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net gain on securities transactions									0	0	0
Income tax expense (benefit)									0	0	0
Net of tax									0	0	0
Post-retirement obligations - Amortization of actuarial losses | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income tax expense (benefit)									49	109	64
Net of tax									(140)	(290)	(179)
Compensation and employee benefits									$ 189	$ 399	$ 243