Loans - Loan Portfolio Composition Including Carrying Value by Segment of Loans Accounted for under ASC Topic 310-30 (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Loans [Line Items]
Total Loans	$ 4,246,941	$ 4,092,308	$ 3,702,334
% of Total	100.00%	100.00%
Commercial Loan [Member]
Loans [Line Items]
Total Loans	$ 2,756,144	$ 2,644,571
% of Total	64.90%	64.60%
Commercial Real Estate [Member]
Loans [Line Items]
Total Loans	$ 645,954	$ 592,212
% of Total	15.20%	14.50%
Residential Real Estate Segment [Member]
Loans [Line Items]
Total Loans	$ 822,652	$ 830,815
% of Total	19.40%	20.30%
Consumer [Member]
Loans [Line Items]
Total Loans	$ 22,191	$ 24,710
% of Total	0.50%	0.60%
ASC 310-30 [Member]
Loans [Line Items]
Total Loans	$ 63,527	$ 70,879	$ 112,309
ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total Loans	19,139	20,398
ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total Loans	36,878	40,393
ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total Loans	7,508	9,995
ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total Loans	2	93
Originated and acquired loans [Member]
Loans [Line Items]
Total Loans	4,183,414	4,021,429
Originated and acquired loans [Member] | Commercial Loan [Member]
Loans [Line Items]
Total Loans	2,737,005	2,624,173
Originated and acquired loans [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total Loans	609,076	551,819
Originated and acquired loans [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total Loans	815,144	820,820
Originated and acquired loans [Member] | Consumer [Member]
Loans [Line Items]
Total Loans	$ 22,189	$ 24,617