Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Net interest income	$ 86,944	$ 86,375
Provision for loan losses	3,099	7,537
Noninterest income	43,785	36,371
Noninterest expense	85,774	80,018
Income before income taxes	41,856	35,191
Income taxes	11,536	11,178
Net income	30,320	24,013
Segment Reporting Information, Additional Elements
Average assets	9,755,006	9,509,306
Depreciation and amortization	6,589	5,853
General Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	85,766	85,241
Provision for loan losses	3,101	7,540
Noninterest income	31,571	23,815
Noninterest expense	75,136	68,820
Income before income taxes	39,100	32,696
Income taxes	10,565	10,304
Net income	28,535	22,392
Segment Reporting Information, Additional Elements
Average assets	9,613,776	9,362,090
Depreciation and amortization	6,223	5,418
Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest income	1,107	1,073
Provision for loan losses	(2)	(3)
Noninterest income	5,588	6,071
Noninterest expense	5,487	5,787
Income before income taxes	1,210	1,360
Income taxes	395	456
Net income	815	904
Segment Reporting Information, Additional Elements
Average assets	77,481	82,465
Depreciation and amortization	47	62
Insurance [Member]
Segment Reporting Information [Line Items]
Net interest income	71	61
Provision for loan losses		0
Noninterest income	6,626	6,485
Noninterest expense	5,151	5,411
Income before income taxes	1,546	1,135
Income taxes	576	418
Net income	970	717
Segment Reporting Information, Additional Elements
Average assets	63,749	64,751
Depreciation and amortization	$ 319	$ 373