Segment Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Segment	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of segments in which the business operates	3
Net interest income	$ 405,336,000	$ 388,487,000	$ 340,990,000
Provision for loan losses, net	7,382,000	(7,382,000)	12,294,000
Noninterest income	173,142,000	173,859,000	175,189,000
Noninterest expense	409,005,000	415,731,000	344,502,000
Income before income taxes	162,091,000	153,997,000	159,383,000
Income taxes	38,529,000	36,937,000	42,100,000
Net Income	123,562,000	117,060,000	117,283,000
Selected Financial Information [Abstract]
Average assets	12,028,030,000	11,530,969,000	9,803,051,000
Depreciation and amortization	36,072,000	37,153,000	29,275,000
General Banking [Member] | Reportable Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	404,214,000	387,586,000	340,130,000
Provision for loan losses, net	7,382,000	(7,382,000)	12,294,000
Noninterest income	107,457,000	113,571,000	122,565,000
Noninterest expense	355,693,000	367,031,000	302,234,000
Income before income taxes	148,596,000	141,508,000	148,167,000
Income taxes	33,726,000	32,499,000	38,079,000
Net Income	114,870,000	109,009,000	110,088,000
Selected Financial Information [Abstract]
Average assets	11,958,078,000	11,463,789,000	9,737,230,000
Depreciation and amortization	35,038,000	35,971,000	27,886,000
Wealth Management [Member] | Reportable Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	851,000	582,000	559,000
Noninterest income	32,209,000	29,446,000	24,421,000
Noninterest expense	26,733,000	24,713,000	20,916,000
Income before income taxes	6,327,000	5,315,000	4,064,000
Income taxes	2,105,000	1,754,000	1,354,000
Net Income	4,222,000	3,561,000	2,710,000
Selected Financial Information [Abstract]
Average assets	1,504,000	304,000	261,000
Depreciation and amortization	190,000	157,000	164,000
Insurance [Member] | Reportable Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	271,000	319,000	301,000
Noninterest income	33,476,000	30,842,000	28,203,000
Noninterest expense	26,579,000	23,987,000	21,352,000
Income before income taxes	7,168,000	7,174,000	7,152,000
Income taxes	2,698,000	2,684,000	2,667,000
Net Income	4,470,000	4,490,000	4,485,000
Selected Financial Information [Abstract]
Average assets	68,448,000	66,876,000	65,560,000
Depreciation and amortization	$ 844,000	$ 1,025,000	$ 1,225,000