Loans, Allowance for Loan Losses and Credit Quality (Allowance Allocations) (Details) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Amortization of Deferred Loan Origination Fees, Net	$ 3,100,000	$ 2,800,000
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	5,307,662,000	4,890,383,000
Ending Balance: Individually Evaluated for Impairment	62,880,000	58,035,000
Financing Receivable, Acquired with Deteriorated Credit Quality	22,576,000	22,315,000
Ending Balance: Total Loans by Group	5,393,118,000	4,970,733,000
Commercial and Industrial [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	823,023,000	856,185,000
Ending Balance: Individually Evaluated for Impairment	6,357,000	4,654,000
Financing Receivable, Acquired with Deteriorated Credit Quality	0	0
Ending Balance: Total Loans by Group	829,380,000	860,839,000
Commercial Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	2,561,984,000	2,304,099,000
Ending Balance: Individually Evaluated for Impairment	32,162,000	30,729,000
Financing Receivable, Acquired with Deteriorated Credit Quality	12,298,000	12,495,000
Ending Balance: Total Loans by Group	2,606,444,000	2,347,323,000
Commercial Construction [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	291,175,000	265,501,000
Ending Balance: Individually Evaluated for Impairment	311,000	311,000
Financing Receivable, Acquired with Deteriorated Credit Quality	180,000	182,000
Ending Balance: Total Loans by Group	291,666,000	265,994,000
Small Business [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	86,682,000	84,159,000
Ending Balance: Individually Evaluated for Impairment	1,027,000	1,088,000
Financing Receivable, Acquired with Deteriorated Credit Quality	0	0
Ending Balance: Total Loans by Group	87,709,000	85,247,000
Residential Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	655,891,000	505,799,000
Ending Balance: Individually Evaluated for Impairment	15,827,000	15,055,000
Financing Receivable, Acquired with Deteriorated Credit Quality	9,661,000	9,405,000
Ending Balance: Total Loans by Group	681,379,000	530,259,000
Consumer Home Equity [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	870,476,000	858,305,000
Ending Balance: Individually Evaluated for Impairment	6,014,000	5,330,000
Financing Receivable, Acquired with Deteriorated Credit Quality	426,000	228,000
Ending Balance: Total Loans by Group	876,916,000	863,863,000
Consumer Other [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	18,431,000	16,335,000
Ending Balance: Individually Evaluated for Impairment	1,182,000	868,000
Financing Receivable, Acquired with Deteriorated Credit Quality	11,000	5,000
Ending Balance: Total Loans by Group	$ 19,624,000	$ 17,208,000

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The net increase(decrease) in interest income during the period representing the allocation of deferred loan origination fees less deferred loan origination costs using the effective interest method over the term of the debt arrangement to which they pertain taking into account the effect of prepayments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Direct Loan Origination Costs

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The balance of financing receivables that were acquired with deteriorated credit quality.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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The balance of financing receivables that were collectively evaluated for impairment.

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The balance of financing receivables that were individually evaluated for impairment.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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-Topic 310

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