Loans and the Allowance for Loan Losses (Details) - Credit quality indicators - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Gross loans	$ 4,205,460	$ 4,174,810
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	811,859	824,082
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	2,632,965	2,592,909
Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	479,190	483,216
Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	278,985	271,795
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	2,461	2,808
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	4,097,526	4,045,989
Pass [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	764,418	767,020
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	2,586,173	2,534,973
Pass [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	470,386	475,066
Pass [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	274,123	266,163
Pass [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	2,426	2,767
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	30,274	43,620
Special Mention [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	13,278	3,764
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	12,350	34,335
Special Mention [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	4,646	5,521
Special Mention [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Special Mention [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	77,660	85,201
Substandard [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	34,163	53,298
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	34,442	23,601
Substandard [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	4,158	2,629
Substandard [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	4,862	5,632
Substandard [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	35	41
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Doubtful [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Doubtful [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Doubtful [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Doubtful [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans
Doubtful [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans