Accumulated Other Comprehensive Income (Loss) (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	$ (2,547)	$ (3,979)	$ (7,984)	$ (11,833)
Other noninterest income	2,124	3,117	6,069	9,096
Salaries and employee benefits	(40,013)	(40,029)	(120,754)	(119,398)
Provision for income taxes	(13,377)	(8,346)	(38,515)	(26,546)
Net income available to common shareholders	25,140	19,327	73,938	53,116
Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Net income available to common shareholders	194	206	560	450
Gains and Losses on Cash Flow Hedges | Amount Reclassified from Accumulated Other Comprehensive Loss | Interest rate contracts
Reclassifications out of accumulated other comprehensive income, net of tax
Interest expense	89	78	230	232
Provision for income taxes	(34)	(30)	(88)	(88)
Net income available to common shareholders	55	48	142	144
Gain and Losses on sales of available for sale securities | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Other noninterest income		90		2
Provision for income taxes		(34)		(1)
Net income available to common shareholders		(56)		(1)
Amortization of defined benefit pension | Amount Reclassified from Accumulated Other Comprehensive Loss
Reclassifications out of accumulated other comprehensive income, net of tax
Salaries and employee benefits	225	165	674	495
Provision for income taxes	(86)	(63)	(256)	(190)
Net income available to common shareholders	$ 139	$ 102	$ 418	$ 305