Accumulated Other Comprehensive Income Amounts reclassified from Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net									$ 1,181	$ 1,581	$ 552
Income before income taxes	$ 43,035	$ 39,608	$ 36,650	$ 30,488	$ 37,338	$ 37,295	$ 31,799	$ 35,188	149,781	141,620	117,785
Income Tax Expense (Benefit)	(12,317)	(12,124)	(11,245)	(9,229)	(10,598)	(11,515)	(9,853)	(10,827)	(44,915)	(42,793)	(36,211)
Net income	$ 30,718	$ 27,484	$ 25,405	$ 21,259	$ 26,740	$ 25,780	$ 21,946	$ 24,361	104,866	98,827	81,574
Compensation and employee benefits									150,282	149,410	130,864
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment securities gains, net									1,181	1,581	552
Income before income taxes									1,181	1,581	552
Income Tax Expense (Benefit)									(429)	(574)	(200)
Net income									752	1,007	352
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes									(668)	(336)	(149)
Income Tax Expense (Benefit)									243	122	54
Net income									(425)	(214)	(95)
Compensation and employee benefits									$ (668)	$ (336)	$ (149)