Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net	$ 1,847	$ 22
Total before tax	56,656	46,785
Income tax provision	(10,785)	(6,815)
Compensation and employee benefits	52,085	50,570
Net income	45,871	39,970
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	(1,847)	102
Total before tax	(1,847)	102
Income tax provision	430	(24)
Net income	(1,417)	78
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	(80)	(80)
Income tax provision	19	19
Compensation and employee benefits	(80)	(80)
Net income	$ (61)	$ (61)