Accumulated Other Comprehensive Income (Reclassification out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net			$ 16,674	$ 2,132
Total before tax	$ 54,683	$ 63,105	117,318	183,579
Income tax provision	(9,949)	(12,378)	(21,374)	(35,257)
Compensation and employee benefits	55,133	54,459	156,018	158,559
Net income	44,734	50,727	95,944	148,322
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	0	0	249	2,132
Total before tax	0	0	249	2,132
Income tax provision	0	0	(58)	(496)
Net income	0	0	191	1,636
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	(104)	(81)	(311)	(240)
Income tax provision	24	19	72	56
Compensation and employee benefits	(104)	(81)	(311)	(240)
Net income	(80)	(62)	(239)	(184)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains and losses from hedging instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	2,673	76	5,803	76
Income tax provision	(621)	(18)	(1,349)	(18)
Net income	2,052	58	4,454	58
Interest income, Loans	$ 2,673	$ 76	$ 5,803	$ 76