Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net			$ (73)	$ 0
Compensation and employee benefits	$ 49,419	$ 39,983	148,938	119,201
Total before tax	57,821	59,107	156,354	137,132
Income tax provision	(11,406)	(18,338)	(28,220)	(40,032)
Net income	46,415	40,769	128,134	97,100
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	0	0	106	0
Total before tax	0	0	106	0
Income tax provision	0	0	(25)	0
Net income	0	0	81	0
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]
Compensation and employee benefits	(80)	(72)	(239)	(279)
Total before tax	(80)	(72)	(239)	(279)
Income tax provision	19	26	56	101
Net income	$ (61)	$ (46)	$ (183)	$ (178)