Loans and Allowance for Loan Losses - Amount of Loans by Loan Category Broken Between Loans Individually and Collectively Evaluated for Impairment and Acquired with Deteriorated Credit Quality (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	$ 9,996	$ 9,373
Collectively evaluated for impairment	3,454,884	3,068,703
Acquired with deteriorated credit quality	73,651	88,835
Gross loans	3,538,531	3,166,911
Commercial and Industrial
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	3,623	1,579
Collectively evaluated for impairment	835,213	711,352
Acquired with deteriorated credit quality	1,603	2,144
Gross loans	840,439	715,075
Construction
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,276	1,289
Collectively evaluated for impairment	483,072	439,309
Acquired with deteriorated credit quality	6,823	7,728
Gross loans	491,171	448,326
Residential Real Estate | 1-to-4 Family Mortgage
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,493	1,262
Collectively evaluated for impairment	532,138	456,229
Acquired with deteriorated credit quality	20,089	23,498
Gross loans	553,720	480,989
Residential Real Estate | Residential Line of Credit
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	253
Collectively evaluated for impairment	214,488	194,986
Gross loans	214,741	194,986
Residential Real Estate | Multi-Family Mortgage
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	187	978
Collectively evaluated for impairment	86,077	61,376
Acquired with deteriorated credit quality		20
Gross loans	86,264	62,374
Commercial Real Estate | Owner Occupied
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	2,035	2,520
Collectively evaluated for impairment	494,631	481,390
Acquired with deteriorated credit quality	7,483	11,962
Gross loans	504,149	495,872
Commercial Real Estate | Non-Owner Occupied
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,049	1,720
Collectively evaluated for impairment	610,724	531,704
Acquired with deteriorated credit quality	16,563	18,164
Gross loans	628,336	551,588
Consumer and Other
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	80	25
Collectively evaluated for impairment	198,541	192,357
Acquired with deteriorated credit quality	21,090	25,319
Gross loans	$ 219,711	$ 217,701