Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	$ 69,434,000	$ 68,734,000	$ 69,434,000	$ 69,334,000
Charge-offs	(5,240,000)	(5,153,000)	(10,070,000)	(12,869,000)
Recoveries	1,174,000	1,201,000	2,408,000	2,659,000
Provision	4,166,000	6,402,000	7,762,000	12,060,000
Balance as of Ending of Period	69,534,000	71,184,000	69,534,000	71,184,000
Allowance for loan losses for acquired loan portfolio	1.5	0
Provision expense and net charge-offs related to acquired loans	100,000	200,000	200,000	400,000
Allowance loan losses [Abstract]
Allowance for loan losses	69,534,000	71,184,000	69,534,000	71,184,000
Allowance for loans individually evaluated for impairment	2,100,000		2,100,000		715,000
Allowance for loans collectively evaluated for impairment	67,434,000		67,434,000		68,719,000
Ending balance of loans	5,574,488,000		5,574,488,000		5,406,795,000
Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	34,437,000	35,358,000	35,090,000	35,624,000
Charge-offs	(1,427,000)	(1,198,000)	(1,906,000)	(4,520,000)
Recoveries	314,000	416,000	713,000	883,000
Provision	1,799,000	3,128,000	1,226,000	5,717,000
Balance as of Ending of Period	35,123,000	37,704,000	35,123,000	37,704,000
Allowance loan losses [Abstract]
Allowance for loan losses	35,123,000	37,704,000	35,123,000	37,704,000
Allowance for loans individually evaluated for impairment	2,100,000		2,100,000		715,000
Allowance for loans collectively evaluated for impairment	33,023,000		33,023,000		34,375,000
Ending balance of loans	2,476,246,000		2,476,246,000		2,392,621,000
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	28,436,000	26,285,000	27,694,000	27,162,000
Charge-offs	(3,648,000)	(3,653,000)	(7,680,000)	(7,376,000)
Recoveries	714,000	696,000	1,455,000	1,673,000
Provision	2,471,000	3,128,000	6,504,000	4,997,000
Balance as of Ending of Period	27,973,000	26,456,000	27,973,000	26,456,000
Allowance loan losses [Abstract]
Allowance for loan losses	27,973,000	26,456,000	27,973,000	26,456,000
Allowance for loans individually evaluated for impairment	0		0		0
Allowance for loans collectively evaluated for impairment	27,973,000		27,973,000		27,694,000
Ending balance of loans	2,025,035,000		2,025,035,000		1,972,537,000
Residential Real Estate Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	6,225,000	6,708,000	6,520,000	6,252,000
Charge-offs	(165,000)	(302,000)	(484,000)	(973,000)
Recoveries	146,000	89,000	240,000	103,000
Provision	(1,000)	311,000	(71,000)	1,424,000
Balance as of Ending of Period	6,205,000	6,806,000	6,205,000	6,806,000
Allowance loan losses [Abstract]
Allowance for loan losses	6,205,000	6,806,000	6,205,000	6,806,000
Allowance for loans individually evaluated for impairment	0		0		0
Allowance for loans collectively evaluated for impairment	6,205,000		6,205,000		6,520,000
Ending balance of loans	1,073,207,000		1,073,207,000		1,041,637,000
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	336,000	383,000	130,000	296,000
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	(103,000)	(165,000)	103,000	(78,000)
Balance as of Ending of Period	233,000	218,000	233,000	218,000
Allowance loan losses [Abstract]
Allowance for loan losses	233,000	218,000	233,000	218,000
Allowance for loans collectively evaluated for impairment	233,000		233,000		130,000
Originated Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	4,728,340,000		4,728,340,000		4,476,403,000
Ending balance of loans individually evaluated for impairment	22,212,000		22,212,000		21,380,000
Ending balance of loans collectively evaluated for impairment	4,706,128,000		4,706,128,000		4,455,023,000
Originated Loans [Member] | Commercial Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	2,098,756,000		2,098,756,000		1,990,232,000
Ending balance of loans individually evaluated for impairment	13,874,000		13,874,000		16,120,000
Ending balance of loans collectively evaluated for impairment	2,084,882,000		2,084,882,000		1,974,112,000
Originated Loans [Member] | Consumer Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	1,845,782,000		1,845,782,000		1,752,950,000
Ending balance of loans individually evaluated for impairment	5,600,000		5,600,000		3,248,000
Ending balance of loans collectively evaluated for impairment	1,840,182,000		1,840,182,000		1,749,702,000
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance loan losses [Abstract]
Ending balance of loans	783,802,000		783,802,000		733,221,000
Ending balance of loans individually evaluated for impairment	2,738,000		2,738,000		2,012,000
Ending balance of loans collectively evaluated for impairment	781,064,000		781,064,000		731,209,000
Acquired Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	846,148,000		846,148,000		930,392,000
Ending balance of loans individually evaluated for impairment	9,672,000		9,672,000		10,060,000
Ending balance of loans collectively evaluated for impairment	836,476,000		836,476,000		920,332,000
Acquired Loans [Member] | Commercial Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	377,490,000		377,490,000		402,389,000
Ending balance of loans individually evaluated for impairment	9,672,000		9,672,000		10,060,000
Ending balance of loans collectively evaluated for impairment	367,818,000		367,818,000		392,329,000
Acquired Loans [Member] | Consumer Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	179,253,000		179,253,000		219,587,000
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	179,253,000		179,253,000		219,587,000
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance loan losses [Abstract]
Ending balance of loans	289,405,000		289,405,000		308,416,000
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	$ 289,405,000		$ 289,405,000		$ 308,416,000