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	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	$ 9,373	$ 12,951	$ 15,576
Collectively evaluated for impairment	3,068,703	1,819,775	1,664,912
Acquired with deteriorated credit quality	88,835	16,058	21,375
Gross loans	3,166,911	1,848,784	1,701,863
Commercial and Industrial
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,579	1,476	1,499
Collectively evaluated for impairment	711,352	384,279	316,418
Acquired with deteriorated credit quality	2,144	478	874
Gross loans	715,075	386,233	318,791
Construction
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,289	2,686	2,866
Collectively evaluated for impairment	439,309	238,900	228,445
Acquired with deteriorated credit quality	7,728	4,319	6,859
Gross loans	448,326	245,905	238,170
Residential Real Estate | 1-to-4 Family Mortgage
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,262	2,471	3,686
Collectively evaluated for impairment	456,229	290,346	284,190
Acquired with deteriorated credit quality	23,498	2,107	2,828
Gross loans	480,989	294,924	290,704
Residential Real Estate | Residential Line of Credit
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment		311
Collectively evaluated for impairment	194,986	176,879	171,526
Gross loans	194,986	177,190	171,526
Residential Real Estate | Multi-Family Mortgage
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	978	1,027	1,074
Collectively evaluated for impairment	61,376	43,922	58,400
Acquired with deteriorated credit quality	20	28	36
Gross loans	62,374	44,977	59,510
Commercial Real Estate | Owner Occupied
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	2,520	2,752	3,000
Collectively evaluated for impairment	481,390	350,812	329,569
Acquired with deteriorated credit quality	11,962	3,782	5,095
Gross loans	495,872	357,346	337,664
Commercial Real Estate | Non-Owner Occupied
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	1,720	2,201	3,451
Collectively evaluated for impairment	531,704	260,361	198,741
Acquired with deteriorated credit quality	18,164	5,340	5,679
Gross loans	551,588	267,902	207,871
Consumer and Other
Accounts Notes And Loans Receivable [Line Items]
Individually evaluated for impairment	25	27
Collectively evaluated for impairment	192,357	74,276	77,623
Acquired with deteriorated credit quality	25,319	4	4
Gross loans	$ 217,701	$ 74,307	$ 77,627