Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net			$ 0	$ 1,174
Compensation and employee benefits	$ 39,983	$ 38,476	119,201	112,086
Total before tax	59,107	39,608	137,132	106,746
Income tax provision	(18,338)	(12,124)	(40,032)	(32,598)
Net income	40,769	27,484	97,100	74,148
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	572	0	1,174
Total before tax	0	572	0	1,174
Income tax provision	0	(208)	0	(426)
Net income	0	364	0	748
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	(72)	(167)	(279)	(501)
Total before tax	(72)	(167)	(279)	(501)
Income tax provision	26	60	101	182
Net income	$ (46)	$ (107)	$ (178)	$ (319)