Loans and the Allowance for Loan Losses (Details) - Credit quality indicators - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Gross loans	$ 4,363,966	$ 4,174,810
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	853,629	824,082
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	2,717,644	2,592,909
Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	498,607	483,216
Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	288,449	271,795
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	5,637	2,808
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	4,257,442	4,045,989
Pass [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	806,912	767,020
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	2,671,130	2,534,973
Pass [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	491,007	475,066
Pass [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	282,784	266,163
Pass [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	5,609	2,767
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	32,844	43,620
Special Mention [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	13,301	3,764
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	16,376	34,335
Special Mention [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	3,167	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	73,680	85,201
Substandard [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	33,416	53,298
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	30,138	23,601
Substandard [Member] | Commercial Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	4,433	2,629
Substandard [Member] | Residential Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	5,665	5,632
Substandard [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Gross loans	28	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