Segment Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Net interest income	$ 348,943,000	$ 352,023,000	$ 354,209,000
Provision for loan losses	30,328,000	49,546,000	77,112,000
Noninterest income	159,854,000	165,927,000	168,242,000
Noninterest expense	329,850,000	325,649,000	308,259,000
Income before income taxes	148,619,000	142,755,000	137,080,000
Income taxes	41,778,000	42,119,000	44,033,000
Net income	106,841,000	100,636,000	93,047,000
Average assets	9,583,443,000	9,291,827,000	9,520,442,000
Depreciation and amortization	25,273,000	25,646,000	26,489,000
Number of reporting segments	3
General Banking [Member]
Segment Reporting Information [Line Items]
Net interest income	344,415,000	347,607,000	349,790,000
Provision for loan losses	30,185,000	49,551,000	77,052,000
Noninterest income	109,601,000	115,934,000	116,335,000
Noninterest expense	284,849,000	283,010,000	264,559,000
Income before income taxes	138,982,000	130,980,000	124,514,000
Income taxes	38,414,000	37,955,000	39,512,000
Net income	100,568,000	93,025,000	85,002,000
Average assets	9,436,557,000	9,136,491,000	9,356,520,000
Depreciation and amortization	23,640,000	23,792,000	24,638,000
Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest income	4,256,000	4,174,000	4,123,000
Provision for loan losses	143,000	(5,000)	60,000
Noninterest income	23,300,000	22,243,000	22,400,000
Noninterest expense	23,300,000	20,459,000	19,644,000
Income before income taxes	4,113,000	5,963,000	6,819,000
Income taxes	1,303,000	1,988,000	2,409,000
Net income	2,810,000	3,975,000	4,410,000
Average assets	81,472,000	89,240,000	95,713,000
Depreciation and amortization	209,000	272,000	295,000
Insurance [Member]
Segment Reporting Information [Line Items]
Net interest income	272,000	242,000	296,000
Noninterest income	26,953,000	27,750,000	29,507,000
Noninterest expense	21,701,000	22,180,000	24,056,000
Income before income taxes	5,524,000	5,812,000	5,747,000
Income taxes	2,061,000	2,176,000	2,112,000
Net income	3,463,000	3,636,000	3,635,000
Average assets	65,414,000	66,096,000	68,209,000
Depreciation and amortization	$ 1,424,000	$ 1,582,000	$ 1,556,000