Loans, Allowance for Loan Losses and Credit Quality (Allowance Allocations) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	5,972,688		$ 5,903,916
Ending Balance: Individually Evaluated for Impairment	73,667		77,297
Financing Receivable, Net	4,391,181		4,355,968
Ending Balance: Total Loans by Group	6,064,366		5,999,605
Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	18,011		18,392
Commercial and Industrial [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	842,891		862,875
Ending Balance: Individually Evaluated for Impairment	38,438		39,178
Financing Receivable, Net	881,329		902,053
Ending Balance: Total Loans by Group	881,329		902,053
Commercial and Industrial [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	0		0
Commercial Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	3,002,407		2,983,642
Ending Balance: Individually Evaluated for Impairment	14,766		16,813
Financing Receivable, Net	3,027,305		3,010,798
Ending Balance: Total Loans by Group	3,027,305		3,010,798
Commercial Real Estate [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	10,132		10,343
Construction Loans [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	356,173		320,391
Ending Balance: Individually Evaluated for Impairment	0		0
Financing Receivable, Net	356,173		320,391
Ending Balance: Total Loans by Group	356,173		320,391
Construction Loans [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	0		0
Small Business [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	125,628		121,855
Ending Balance: Individually Evaluated for Impairment	746		871
Financing Receivable, Net	126,374		122,726
Ending Balance: Total Loans by Group	126,374		122,726
Small Business [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	0		0
Residential Real Estate [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	632,634		622,392
Ending Balance: Individually Evaluated for Impairment	13,674		14,175
Ending Balance: Total Loans by Group	653,999		644,426
Residential Real Estate [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	7,691		7,859
Consumer Home Equity [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	1,002,898		982,095
Ending Balance: Individually Evaluated for Impairment	5,685		5,863
Ending Balance: Total Loans by Group	1,008,771		988,147
Consumer Home Equity [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	188		189
Consumer Other [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Ending Balance: Collectively Evaluated for Impairment	10,057		10,666
Ending Balance: Individually Evaluated for Impairment	358		397
Ending Balance: Total Loans by Group	10,415		11,064
Consumer Other [Member] \| Receivables Acquired with Deteriorated Credit Quality [Member]
Allowance for loans based on collective and individual evaluation of impairment by loan category
Financing Receivable, Net	$ 0		$ 1

Allowance for loans based on collective and individual evaluation of impairment by loan category.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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

+ References

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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953682-111524

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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