Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	$ 69,534,000	$ 71,184,000	$ 69,434,000	$ 69,334,000
Charge-offs	(5,977,000)	(7,609,000)	(16,047,000)	(20,478,000)
Recoveries	892,000	1,411,000	3,300,000	4,070,000
Provision	4,885,000	5,198,000	12,647,000	17,258,000
Balance as of Ending of Period	69,334,000	70,184,000	69,334,000	70,184,000
Allowance for loan losses for acquired loan portfolio	3.0	0
Provision expense and net charge-offs related to acquired loans	300,000	100,000	500,000	500,000
Allowance loan losses [Abstract]
Allowance for loan losses	69,334,000	70,184,000	69,334,000	70,184,000
Allowance for loans individually evaluated for impairment	3,600,000		3,600,000		715,000
Allowance for loans collectively evaluated for impairment	65,734,000		65,734,000		68,719,000
Ending balance of loans	5,587,091,000		5,587,091,000		5,406,795,000
Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	35,123,000	37,704,000	35,090,000	35,624,000
Charge-offs	(1,517,000)	(3,489,000)	(3,423,000)	(8,009,000)
Recoveries	253,000	602,000	966,000	1,485,000
Provision	1,779,000	980,000	3,005,000	6,697,000
Balance as of Ending of Period	35,638,000	35,797,000	35,638,000	35,797,000
Allowance loan losses [Abstract]
Allowance for loan losses	35,638,000	35,797,000	35,638,000	35,797,000
Allowance for loans individually evaluated for impairment	3,600,000		3,600,000		715,000
Allowance for loans collectively evaluated for impairment	32,038,000		32,038,000		34,375,000
Ending balance of loans	2,457,906,000		2,457,906,000		2,392,621,000
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	27,973,000	26,456,000	27,694,000	27,162,000
Charge-offs	(3,979,000)	(3,746,000)	(11,659,000)	(11,122,000)
Recoveries	632,000	733,000	2,087,000	2,406,000
Provision	2,826,000	3,744,000	9,330,000	8,741,000
Balance as of Ending of Period	27,452,000	27,187,000	27,452,000	27,187,000
Allowance loan losses [Abstract]
Allowance for loan losses	27,452,000	27,187,000	27,452,000	27,187,000
Allowance for loans individually evaluated for impairment	0		0		0
Allowance for loans collectively evaluated for impairment	27,452,000		27,452,000		27,694,000
Ending balance of loans	2,029,046,000		2,029,046,000		1,972,537,000
Residential Real Estate Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	6,205,000	6,806,000	6,520,000	6,252,000
Charge-offs	(481,000)	(374,000)	(965,000)	(1,347,000)
Recoveries	7,000	76,000	247,000	179,000
Provision	212,000	402,000	141,000	1,826,000
Balance as of Ending of Period	5,943,000	6,910,000	5,943,000	6,910,000
Allowance loan losses [Abstract]
Allowance for loan losses	5,943,000	6,910,000	5,943,000	6,910,000
Allowance for loans individually evaluated for impairment	0		0		0
Allowance for loans collectively evaluated for impairment	5,943,000		5,943,000		6,520,000
Ending balance of loans	1,100,139,000		1,100,139,000		1,041,637,000
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	233,000	218,000	130,000	296,000
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	68,000	72,000	171,000	(6,000)
Balance as of Ending of Period	301,000	290,000	301,000	290,000
Allowance loan losses [Abstract]
Allowance for loan losses	301,000	290,000	301,000	290,000
Allowance for loans collectively evaluated for impairment	301,000		301,000		130,000
Originated Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	4,788,900,000		4,788,900,000		4,476,403,000
Ending balance of loans individually evaluated for impairment	22,097,000		22,097,000		21,380,000
Ending balance of loans collectively evaluated for impairment	4,766,803,000		4,766,803,000		4,455,023,000
Originated Loans [Member] | Commercial Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	2,100,493,000		2,100,493,000		1,990,232,000
Ending balance of loans individually evaluated for impairment	13,625,000		13,625,000		16,120,000
Ending balance of loans collectively evaluated for impairment	2,086,868,000		2,086,868,000		1,974,112,000
Originated Loans [Member] | Consumer Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	1,866,027,000		1,866,027,000		1,752,950,000
Ending balance of loans individually evaluated for impairment	5,343,000		5,343,000		3,248,000
Ending balance of loans collectively evaluated for impairment	1,860,684,000		1,860,684,000		1,749,702,000
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance loan losses [Abstract]
Ending balance of loans	822,380,000		822,380,000		733,221,000
Ending balance of loans individually evaluated for impairment	3,129,000		3,129,000		2,012,000
Ending balance of loans collectively evaluated for impairment	819,251,000		819,251,000		731,209,000
Acquired Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	798,191,000		798,191,000		930,392,000
Ending balance of loans individually evaluated for impairment	9,396,000		9,396,000		10,060,000
Ending balance of loans collectively evaluated for impairment	788,795,000		788,795,000		920,332,000
Acquired Loans [Member] | Commercial Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	357,413,000		357,413,000		402,389,000
Ending balance of loans individually evaluated for impairment	9,396,000		9,396,000		10,060,000
Ending balance of loans collectively evaluated for impairment	348,017,000		348,017,000		392,329,000
Acquired Loans [Member] | Consumer Loans [Member]
Allowance loan losses [Abstract]
Ending balance of loans	163,019,000		163,019,000		219,587,000
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	163,019,000		163,019,000		219,587,000
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance loan losses [Abstract]
Ending balance of loans	277,759,000		277,759,000		308,416,000
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans collectively evaluated for impairment	$ 277,759,000		$ 277,759,000		$ 308,416,000