Allowance for Loan Losses (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
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				$ 36,072				$ 28,936	$ 36,072	$ 28,936	$ 21,296
Charge-offs									(7,853)	(1,955)	(1,362)
Recoveries									344	935	362
Provisions for (reduction in) loan losses	$ 2,297	$ 1,562	$ 334	1,526	$ 2,258	$ 1,981	$ 1,761	2,253	7,135	8,156	8,640
Balance, at the end of the period	35,698				36,072				35,698	36,072	28,936
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				584				0	584	55
General portfolio allocation	35,698				35,488				35,698	35,488	28,881
Loans individually evaluated for impairment	22,989				12,458				$ 22,989	$ 12,458	$ 3,284
Specific reserves to total loans individually evaluated for impairment									0.00%	4.69%	1.67%
Loans collectively evaluated for impairment	8,708,909				8,833,828				$ 8,708,909	$ 8,833,828	$ 6,195,343
General reserves to total loans collectively evaluated for impairment									0.41%	0.40%	0.47%
Total gross loans	8,731,898				8,846,286				$ 8,731,898	$ 8,846,286	$ 6,198,627
Total allowance to gross loans									0.41%	0.41%	0.47%
Owner Occupied Commercial Real Estate Loans Commercial and Industrial Loans and Small Business Administration Loans
Allowance for Loan Losses
Period one considered for comparison of allowance for loan losses factor									1 year
Period considered for comparison of allowance for loan losses factor									1 year 7 months 6 days
Business Loans | Commercial and industrial
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				10,821				9,721	$ 10,821	$ 9,721	$ 6,362
Charge-offs									(2,318)	(1,411)	(1,344)
Recoveries									189	698	94
Provisions for (reduction in) loan losses									2,642	1,813	4,609
Balance, at the end of the period	11,334				10,821				11,334	10,821	9,721
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				118				0	118	0
General portfolio allocation	11,334				10,703				11,334	10,703	9,721
Loans individually evaluated for impairment	7,529				1,023				$ 7,529	$ 1,023	$ 1,160
Specific reserves to total loans individually evaluated for impairment									0.00%	11.53%	0.00%
Loans collectively evaluated for impairment	1,257,656				1,363,400				$ 1,257,656	$ 1,363,400	$ 1,085,499
General reserves to total loans collectively evaluated for impairment									0.90%	0.79%	0.90%
Total gross loans	1,265,185				1,364,423				$ 1,265,185	$ 1,364,423	$ 1,086,659
Total allowance to gross loans									0.90%	0.79%	0.89%
Business Loans | Franchise
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				6,500				5,797	$ 6,500	$ 5,797	$ 3,845
Charge-offs									(2,531)	0	0
Recoveries									18	0	0
Provisions for (reduction in) loan losses									2,421	703	1,952
Balance, at the end of the period	6,408				6,500				6,408	6,500	5,797
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	6,408				6,500				6,408	6,500	5,797
Loans individually evaluated for impairment	10,834				189				$ 10,834	$ 189	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	906,041				765,227				$ 906,041	$ 765,227	$ 660,414
General reserves to total loans collectively evaluated for impairment									0.71%	0.85%	0.88%
Total gross loans	916,875				765,416				$ 916,875	$ 765,416	$ 660,414
Total allowance to gross loans									0.70%	0.85%	0.88%
Business Loans | Commercial owner occupied
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				1,386				767	$ 1,386	$ 767	$ 1,193
Charge-offs									(125)	(33)	0
Recoveries									46	47	105
Provisions for (reduction in) loan losses									616	605	(531)
Balance, at the end of the period	1,923				1,386				1,923	1,386	767
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	55
General portfolio allocation	1,923				1,386				1,923	1,386	712
Loans individually evaluated for impairment	0				599				$ 0	$ 599	$ 97
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	56.70%
Loans collectively evaluated for impairment	1,674,092				1,678,523				$ 1,674,092	$ 1,678,523	$ 1,289,116
General reserves to total loans collectively evaluated for impairment									0.11%	0.08%	0.06%
Total gross loans	1,674,092				1,679,122				$ 1,674,092	$ 1,679,122	$ 1,289,213
Total allowance to gross loans									0.11%	0.08%	0.06%
Business Loans | SBA
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				4,288				2,890	$ 4,288	$ 2,890	$ 1,039
Charge-offs									(2,238)	(102)	(8)
Recoveries									78	169	127
Provisions for (reduction in) loan losses									2,351	1,331	1,732
Balance, at the end of the period	4,479				4,288				4,479	4,288	2,890
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				466				0	466	0
General portfolio allocation	4,479				3,822				4,479	3,822	2,890
Loans individually evaluated for impairment	3,132				2,739				$ 3,132	$ 2,739	$ 1,201
Specific reserves to total loans individually evaluated for impairment									0.00%	17.01%	0.00%
Loans collectively evaluated for impairment	172,683				191,143				$ 172,683	$ 191,143	$ 184,313
General reserves to total loans collectively evaluated for impairment									2.59%	2.00%	1.57%
Total gross loans	175,815				193,882				$ 175,815	$ 193,882	$ 185,514
Total allowance to gross loans									2.55%	2.21%	1.56%
Business Loans | Agribusiness
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				3,283				1,291	$ 3,283	$ 1,291	$ 0
Charge-offs									0	0	0
Recoveries									0	0	0
Provisions for (reduction in) loan losses									(760)	1,992	1,291
Balance, at the end of the period	2,523				3,283				2,523	3,283	1,291
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	2,523				3,283				2,523	3,283	1,291
Loans individually evaluated for impairment	0				7,500				$ 0	$ 7,500	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	127,834				131,019				$ 127,834	$ 131,019	$ 116,066
General reserves to total loans collectively evaluated for impairment									1.97%	2.51%	1.11%
Total gross loans	127,834				138,519				$ 127,834	$ 138,519	$ 116,066
Total allowance to gross loans									1.97%	2.37%	1.11%
Real Estate Loans | Commercial non-owner occupied
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				1,604				1,266	$ 1,604	$ 1,266	$ 1,715
Charge-offs									(625)	0	0
Recoveries									0	0	0
Provisions for (reduction in) loan losses									920	338	(449)
Balance, at the end of the period	1,899				1,604				1,899	1,604	1,266
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	1,899				1,604				1,899	1,604	1,266
Loans individually evaluated for impairment	1,128				0				$ 1,128	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	2,071,246				2,003,174				$ 2,071,246	$ 2,003,174	$ 1,243,115
General reserves to total loans collectively evaluated for impairment									0.09%	0.08%	0.10%
Total gross loans	2,072,374				2,003,174				$ 2,072,374	$ 2,003,174	$ 1,243,115
Total allowance to gross loans									0.09%	0.08%	0.10%
Real Estate Loans | Multi-family
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				725				607	$ 725	$ 607	$ 2,927
Charge-offs									0	0	0
Recoveries									0	0	0
Provisions for (reduction in) loan losses									4	118	(2,320)
Balance, at the end of the period	729				725				729	725	607
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	729				725				729	725	607
Loans individually evaluated for impairment	0				0				$ 0	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	1,576,870				1,535,289				$ 1,576,870	$ 1,535,289	$ 794,384
General reserves to total loans collectively evaluated for impairment									0.05%	0.05%	0.08%
Total gross loans	1,576,870				1,535,289				$ 1,576,870	$ 1,535,289	$ 794,384
Total allowance to gross loans									0.05%	0.05%	0.08%
Real Estate Loans | One-to-four family
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				805				803	$ 805	$ 803	$ 365
Charge-offs									0	0	(10)
Recoveries									2	13	35
Provisions for (reduction in) loan losses									(152)	(11)	413
Balance, at the end of the period	655				805				655	805	803
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	655				805				655	805	803
Loans individually evaluated for impairment	366				408				$ 366	$ 408	$ 817
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	254,413				355,856				$ 254,413	$ 355,856	$ 270,077
General reserves to total loans collectively evaluated for impairment									0.26%	0.23%	0.30%
Total gross loans	254,779				356,264				$ 254,779	$ 356,264	$ 270,894
Total allowance to gross loans									0.26%	0.23%	0.30%
Real Estate Loans | Construction
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				5,166				4,569	$ 5,166	$ 4,569	$ 3,632
Charge-offs									0	0	0
Recoveries									0	0	0
Provisions for (reduction in) loan losses									(1,357)	597	937
Balance, at the end of the period	3,809				5,166				3,809	5,166	4,569
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	3,809				5,166				3,809	5,166	4,569
Loans individually evaluated for impairment	0				0				$ 0	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	410,065				523,643				$ 410,065	$ 523,643	$ 282,811
General reserves to total loans collectively evaluated for impairment									0.93%	0.99%	1.62%
Total gross loans	410,065				523,643				$ 410,065	$ 523,643	$ 282,811
Total allowance to gross loans									0.93%	0.99%	1.62%
Real Estate Loans | Farmland
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				503				137	$ 503	$ 137	$ 0
Charge-offs									0	0	0
Recoveries									0	0	0
Provisions for (reduction in) loan losses									355	366	137
Balance, at the end of the period	858				503				858	503	137
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	858				503				858	503	137
Loans individually evaluated for impairment	0				0				$ 0	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	175,997				150,502				$ 175,997	$ 150,502	$ 145,393
General reserves to total loans collectively evaluated for impairment									0.49%	0.33%	0.09%
Total gross loans	175,997				150,502				$ 175,997	$ 150,502	$ 145,393
Total allowance to gross loans									0.49%	0.33%	0.09%
Real Estate Loans | Land
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				772				993	$ 772	$ 993	$ 198
Charge-offs									0	0	0
Recoveries									0	0	0
Provisions for (reduction in) loan losses									(97)	(221)	795
Balance, at the end of the period	675				772				675	772	993
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	675				772				675	772	993
Loans individually evaluated for impairment	0				0				$ 0	$ 0	$ 9
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	31,090				46,628				$ 31,090	$ 46,628	$ 31,224
General reserves to total loans collectively evaluated for impairment									2.17%	1.66%	3.18%
Total gross loans	31,090				46,628				$ 31,090	$ 46,628	$ 31,233
Total allowance to gross loans									2.17%	1.66%	3.18%
Consumer Loans | Consumer loans
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period				$ 219				$ 95	$ 219	$ 95	$ 20
Charge-offs									(16)	(409)	0
Recoveries									11	8	1
Provisions for (reduction in) loan losses									192	525	74
Balance, at the end of the period	406				219				406	219	95
Amount of allowance attributed to:
Specifically evaluated impaired loans	0				0				0	0	0
General portfolio allocation	406				219				406	219	95
Loans individually evaluated for impairment	0				0				$ 0	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment									0.00%	0.00%	0.00%
Loans collectively evaluated for impairment	50,922				89,424				$ 50,922	$ 89,424	$ 92,931
General reserves to total loans collectively evaluated for impairment									0.80%	0.24%	0.10%
Total gross loans	$ 50,922				$ 89,424				$ 50,922	$ 89,424	$ 92,931
Total allowance to gross loans									0.80%	0.24%	0.10%