Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net			$ 2,132	$ (73)
Total before tax	$ 63,105	$ 57,821	183,579	156,354
Income tax provision	(12,378)	(11,406)	(35,257)	(28,220)
Compensation and employee benefits	54,459	49,419	158,559	148,938
Net income	50,727	46,415	148,322	128,134
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	0	0	2,132	106
Total before tax	0	0	2,132	106
Income tax provision	0	0	(496)	(25)
Net income	0	0	1,636	81
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Pension Plan Liability [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(81)	(80)	(240)	(239)
Income tax provision	19	19	56	56
Compensation and employee benefits	(81)	(80)	(240)	(239)
Net income	(62)	(61)	(184)	(183)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains and losses from hedging instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	76	0	76	0
Income tax provision	(18)	0	(18)	0
Net income	58	0	58	0
Interest income	$ 76	$ 0	$ 76	$ 0