Loans and the Allowance for Loan Losses (Details) - Composition of loan portfolio - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 4,205,460	$ 4,174,810
Net deferred loan fees	(2,781)	(3,354)
Total loans receivable	4,202,679	4,171,456
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	811,859	824,082
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	2,632,965	2,592,909
Commercial Construction Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	479,190	483,216
Residential Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	278,985	271,795
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 2,461	$ 2,808