Loans and the Allowance for Loan Losses (Details) - Composition of loan portfolio - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 4,363,966	$ 4,174,810
Net deferred loan fees	(3,112)	(3,354)
Total loans receivable	4,360,854	4,171,456
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	853,629	824,082
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	2,717,644	2,592,909
Commercial Construction Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	498,607	483,216
Residential Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	288,449	271,795
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 5,637	$ 2,808