Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	$ 65,359,000	$ 69,434,000	$ 66,359,000	$ 69,434,000
Charge-offs	(5,368,000)	(5,240,000)	(11,048,000)	(10,070,000)
Recoveries	1,070,000	1,174,000	2,108,000	2,408,000
Provision	3,898,000	4,166,000	7,540,000	7,762,000
Balance as of Ending of Period	64,959,000	69,534,000	64,959,000	69,534,000
Allowance for loan losses for acquired loan portfolio	1.9	1.5
Provision expense and net charge-offs related to acquired loans	100,000	100,000	700,000	200,000
Allowance loan losses [Abstract]
Allowance for loan losses	65,359,000	69,434,000	66,359,000	69,434,000	$ 64,959,000	$ 66,359,000
Allowance for loans individually evaluated for impairment					2,885,000	1,100,000
Allowance for loans collectively evaluated for impairment					62,074,000	65,259,000
Ending balance of loans	5,770,888,000		5,770,888,000
Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	31,278,000	34,437,000	32,433,000	35,090,000
Charge-offs	(584,000)	(1,427,000)	(1,382,000)	(1,906,000)
Recoveries	280,000	314,000	514,000	713,000
Provision	(2,648,000)	1,799,000	(3,239,000)	1,226,000
Balance as of Ending of Period	28,326,000	35,123,000	28,326,000	35,123,000
Allowance loan losses [Abstract]
Allowance for loan losses	31,278,000	34,437,000	32,433,000	35,090,000	28,326,000	32,433,000
Allowance for loans individually evaluated for impairment					2,885,000	1,100,000
Allowance for loans collectively evaluated for impairment					25,441,000	31,333,000
Ending balance of loans	2,565,590,000		2,565,590,000
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	26,156,000	28,436,000	26,720,000	27,694,000
Charge-offs	(4,275,000)	(3,648,000)	(8,653,000)	(7,680,000)
Recoveries	697,000	714,000	1,445,000	1,455,000
Provision	5,736,000	2,471,000	8,802,000	6,504,000
Balance as of Ending of Period	28,314,000	27,973,000	28,314,000	27,973,000
Allowance loan losses [Abstract]
Allowance for loan losses	26,156,000	28,436,000	26,720,000	27,694,000	28,314,000	26,720,000
Allowance for loans individually evaluated for impairment					0	0
Allowance for loans collectively evaluated for impairment					28,314,000	26,720,000
Ending balance of loans	2,051,540,000		2,051,540,000
Residential Real Estate Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	7,698,000	6,225,000	7,130,000	6,520,000
Charge-offs	(509,000)	(165,000)	(1,013,000)	(484,000)
Recoveries	93,000	146,000	149,000	240,000
Provision	999,000	(1,000)	2,015,000	(71,000)
Balance as of Ending of Period	8,281,000	6,205,000	8,281,000	6,205,000
Allowance loan losses [Abstract]
Allowance for loan losses	7,698,000	6,225,000	7,130,000	6,520,000	8,281,000	7,130,000
Allowance for loans individually evaluated for impairment					0	0
Allowance for loans collectively evaluated for impairment					8,281,000	7,130,000
Ending balance of loans	1,153,758,000		1,153,758,000
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	227,000	336,000	76,000	130,000
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	(189,000)	(103,000)	(38,000)	103,000
Balance as of Ending of Period	38,000	233,000	38,000	233,000
Allowance loan losses [Abstract]
Allowance for loan losses	227,000	$ 336,000	76,000	$ 130,000	38,000	76,000
Allowance for loans collectively evaluated for impairment					$ 38,000	$ 76,000
Originated Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	5,079,403,000		5,079,403,000
Ending balance of loans individually evaluated for impairment	24,494,000		24,494,000
Ending balance of loans collectively evaluated for impairment	5,054,909,000		5,054,909,000
Originated Loans [Member] | Commercial Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	2,246,172,000		2,246,172,000
Ending balance of loans individually evaluated for impairment	12,506,000		12,506,000
Ending balance of loans collectively evaluated for impairment	2,233,666,000		2,233,666,000
Originated Loans [Member] | Consumer Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	1,931,224,000		1,931,224,000
Ending balance of loans individually evaluated for impairment	6,967,000		6,967,000
Ending balance of loans collectively evaluated for impairment	1,924,257,000		1,924,257,000
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance loan losses [Abstract]
Ending balance of loans	902,007,000		902,007,000
Ending balance of loans individually evaluated for impairment	5,021,000		5,021,000
Ending balance of loans collectively evaluated for impairment	896,986,000		896,986,000
Acquired Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	691,485,000		691,485,000
Ending balance of loans individually evaluated for impairment	9,719,000		9,719,000
Ending balance of loans collectively evaluated for impairment	681,766,000		681,766,000
Acquired Loans [Member] | Commercial Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	319,418,000		319,418,000
Ending balance of loans individually evaluated for impairment	9,719,000		9,719,000
Ending balance of loans collectively evaluated for impairment	309,699,000		309,699,000
Acquired Loans [Member] | Consumer Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	120,316,000		120,316,000
Ending balance of loans individually evaluated for impairment	0		0
Ending balance of loans collectively evaluated for impairment	120,316,000		120,316,000
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance loan losses [Abstract]
Ending balance of loans	251,751,000		251,751,000
Ending balance of loans individually evaluated for impairment	0		0
Ending balance of loans collectively evaluated for impairment	$ 251,751,000		$ 251,751,000