Allowance for Loan Losses - Activity in Allowance for Losses Disaggregated on Basis of Impairment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				$ 35,042				$ 32,086	$ 35,042	$ 32,086	$ 31,083
Charge-offs									(4,989)	(3,605)	(4,838)
Recoveries									1,807	1,432	1,621
Provision for loan losses	$ 1,558	$ 466	$ 1,367	920	$ 1,162	$ 1,065	$ 1,750	1,152	4,311	5,129	4,220
Balance at the end of the year	36,171				35,042				36,171	35,042	32,086
Commercial business
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				23,711				21,999	23,711	21,999	22,382
Charge-offs									(2,692)	(1,400)	(2,438)
Recoveries									657	908	947
Provision for loan losses									2,257	2,204	1,108
Balance at the end of the year	23,933				23,711				23,933	23,711	21,999
Commercial business | Commercial and industrial
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				11,343				9,910	11,343	9,910	10,968
Charge-offs									(2,692)	(1,250)	(859)
Recoveries									166	901	792
Provision for loan losses									2,922	1,782	(991)
Balance at the end of the year	11,739				11,343				11,739	11,343	9,910
Commercial business | Owner-occupied commercial real estate
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				4,898				3,992	4,898	3,992	3,661
Charge-offs									0	(1)	(1,579)
Recoveries									50	7	155
Provision for loan losses									(436)	900	1,755
Balance at the end of the year	4,512				4,898				4,512	4,898	3,992
Commercial business | Non-owner occupied commercial real estate
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				7,470				8,097	7,470	8,097	7,753
Charge-offs									0	(149)	0
Recoveries									441	0	0
Provision for loan losses									(229)	(478)	344
Balance at the end of the year	7,682				7,470				7,682	7,470	8,097
One-to-four family residential
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				1,203				1,056	1,203	1,056	1,015
Charge-offs									(60)	(45)	(30)
Recoveries									0	0	2
Provision for loan losses									315	192	69
Balance at the end of the year	1,458				1,203				1,458	1,203	1,056
Real estate construction and land development
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				2,194				2,052	2,194	2,052	2,156
Charge-offs									(133)	0	(556)
Recoveries									637	11	202
Provision for loan losses									362	131	250
Balance at the end of the year	3,060				2,194				3,060	2,194	2,052
Real estate construction and land development | One-to-four family residential
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				1,240				862	1,240	862	797
Charge-offs									(133)	0	(556)
Recoveries									637	11	202
Provision for loan losses									(289)	367	419
Balance at the end of the year	1,455				1,240				1,455	1,240	862
Real estate construction and land development | Five or more family residential and commercial properties
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				954				1,190	954	1,190	1,359
Charge-offs									0	0	0
Recoveries									0	0	0
Provision for loan losses									651	(236)	(169)
Balance at the end of the year	1,605				954				1,605	954	1,190
Consumer
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				6,581				6,081	6,581	6,081	5,024
Charge-offs									(2,104)	(2,160)	(1,814)
Recoveries									513	513	470
Provision for loan losses									1,831	2,147	2,401
Balance at the end of the year	6,821				6,581				6,821	6,581	6,081
Unallocated
Schedule of allowance for loan losses on the basis of impairment method
Balance at the beginning of the year				$ 1,353				$ 898	1,353	898	506
Charge-offs									0	0	0
Recoveries									0	0	0
Provision for loan losses									(454)	455	392
Balance at the end of the year	$ 899				$ 1,353				$ 899	$ 1,353	$ 898