Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	$ 22	$ 0
Compensation and employee benefits	50,570	40,825
Total before tax	46,785	39,773
Income tax provision	(6,815)	(10,574)
Net income	39,970	29,199
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	102	0
Total before tax	102	0
Income tax provision	(24)	0
Net income	78	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)	(136)
Total before tax	(80)	(136)
Income tax provision	19	49
Net income	$ (61)	$ (87)