Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net			$ (11)	$ 0
Compensation and employee benefits	$ 48,949	$ 38,393	99,519	79,218
Total before tax	51,748	38,252	98,533	78,025
Income tax provision	(9,999)	(11,120)	(16,814)	(21,694)
Net income	41,749	27,132	81,719	56,331
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	5	0	107	0
Total before tax	5	0	107	0
Income tax provision	(1)	0	(25)	0
Net income	4	0	82	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)	(71)	(160)	(207)
Total before tax	(80)	(71)	(160)	(207)
Income tax provision	19	26	38	75
Net income	$ (61)	$ (45)	$ (122)	$ (132)