Loans and Allowance for Loan Losses - Amount of Loans by Loan Category Broken Out Between Loans Individually Evaluated for Impairment and Collectively Evaluated for Impairment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	$ 8,921	$ 12,951
Collectively evaluated for impairment	3,013,186	1,819,775
Acquired with deteriorated credit quality	92,455	16,058
Gross loans	3,114,562	1,848,784
Commercial and Industrial
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	826	1,476
Collectively evaluated for impairment	727,885	384,279
Acquired with deteriorated credit quality	2,877	478
Gross loans	731,588	386,233
Construction
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,295	2,686
Collectively evaluated for impairment	426,039	238,900
Acquired with deteriorated credit quality	8,080	4,319
Gross loans	435,414	245,905
Residential Real Estate | 1-to-4 Family Mortgage
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,272	2,471
Collectively evaluated for impairment	433,544	290,346
Acquired with deteriorated credit quality	24,651	2,107
Gross loans	459,467	294,924
Residential Real Estate | Residential Line of Credit
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment		311
Collectively evaluated for impairment	188,392	176,879
Gross loans	188,392	177,190
Residential Real Estate | Multi-Family Mortgage
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	988	1,027
Collectively evaluated for impairment	72,994	43,922
Acquired with deteriorated credit quality	22	28
Gross loans	74,004	44,977
Commercial Real Estate | Owner Occupied
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	2,785	2,752
Collectively evaluated for impairment	459,537	350,812
Acquired with deteriorated credit quality	11,073	3,782
Gross loans	473,395	357,346
Commercial Real Estate | Non-Owner Occupied
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,732	2,201
Collectively evaluated for impairment	500,713	260,361
Acquired with deteriorated credit quality	18,971	5,340
Gross loans	521,416	267,902
Consumer and Other
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	23	27
Collectively evaluated for impairment	204,082	74,276
Acquired with deteriorated credit quality	26,781	4
Gross loans	$ 230,886	$ 74,307