Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	$ 37,856	$ 30,502	$ 36,072	$ 28,936
Charge-offs	(3,636)	(273)	(3,943)	(1,019)
Recoveries	64	165	143	224
Provisions for (reduction in) loan losses	742	1,353	2,754	3,606
Balance, at the end of the period	35,026	31,747	35,026	31,747
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	$ 584
Amount of allowance attributed to: General portfolio allocation	35,026	31,747	35,026	31,747
Loans individually evaluated for impairment	15,103	6,039	$ 15,103	$ 6,039
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	8,766,803	6,274,810	$ 8,766,803	$ 6,274,810
General reserves to total loans collectively evaluated for impairment			0.40%	0.51%
Gross loans, excluding loan receivable held for sale	8,781,906	6,280,849	$ 8,781,906	$ 6,280,849
Total allowance to gross loans			0.40%	0.51%
Business loans | Commercial and industrial
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	10,450	9,492	$ 10,821	$ 9,721
Charge-offs	(393)	(246)	(695)	(911)
Recoveries	47	138	114	163
Provisions for (reduction in) loan losses	927	780	791	1,191
Balance, at the end of the period	11,031	10,164	11,031	10,164
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	118
Amount of allowance attributed to: General portfolio allocation	11,031	10,164	11,031	10,164
Loans individually evaluated for impairment	2,935	1,062	$ 2,935	$ 1,062
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	1,297,148	1,101,524	$ 1,297,148	$ 1,101,524
General reserves to total loans collectively evaluated for impairment			0.85%	0.92%
Gross loans, excluding loan receivable held for sale	1,300,083	1,102,586	$ 1,300,083	$ 1,102,586
Total allowance to gross loans			0.85%	0.92%
Business loans | Franchise
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	7,871	6,095	$ 6,500	$ 5,797
Charge-offs	(1,536)	0	(1,536)	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	430	86	1,801	384
Balance, at the end of the period	6,765	6,181	6,765	6,181
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	6,765	6,181	6,765	6,181
Loans individually evaluated for impairment	697	209	$ 697	$ 209
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	859,602	708,748	$ 859,602	$ 708,748
General reserves to total loans collectively evaluated for impairment			0.79%	0.87%
Gross loans, excluding loan receivable held for sale	860,299	708,957	$ 860,299	$ 708,957
Total allowance to gross loans			0.79%	0.87%
Business loans | Commercial owner occupied
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	1,305	791	$ 1,386	$ 767
Charge-offs	0	0	0	0
Recoveries	15	16	23	24
Provisions for (reduction in) loan losses	170	330	81	346
Balance, at the end of the period	1,490	1,137	1,490	1,137
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	1,490	1,137	1,490	1,137
Loans individually evaluated for impairment	564	0	$ 564	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	1,667,348	1,310,722	$ 1,667,348	$ 1,310,722
General reserves to total loans collectively evaluated for impairment			0.09%	0.09%
Gross loans, excluding loan receivable held for sale	1,667,912	1,310,722	$ 1,667,912	$ 1,310,722
Total allowance to gross loans			0.09%	0.09%
Business loans | SBA
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	5,173	2,814	$ 4,288	$ 2,890
Charge-offs	(1,219)	(27)	(1,219)	(56)
Recoveries	1	9	4	35
Provisions for (reduction in) loan losses	(592)	(221)	290	(294)
Balance, at the end of the period	3,363	2,575	3,363	2,575
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	466
Amount of allowance attributed to: General portfolio allocation	3,363	2,575	3,363	2,575
Loans individually evaluated for impairment	2,338	1,423	$ 2,338	$ 1,423
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	178,025	175,273	$ 178,025	$ 175,273
General reserves to total loans collectively evaluated for impairment			1.89%	1.47%
Gross loans, excluding loan receivable held for sale	180,363	176,696	$ 180,363	$ 176,696
Total allowance to gross loans			1.86%	1.46%
Business loans | Agribusiness
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	3,137	2,105	$ 3,283	$ 1,291
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	(372)	589	(518)	1,403
Balance, at the end of the period	2,765	2,694	2,765	2,694
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	2,765	2,694	2,765	2,694
Loans individually evaluated for impairment	7,466	0	$ 7,466	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	119,391	136,962	$ 119,391	$ 136,962
General reserves to total loans collectively evaluated for impairment			2.32%	1.97%
Gross loans, excluding loan receivable held for sale	126,857	136,962	$ 126,857	$ 136,962
Total allowance to gross loans			2.18%	1.97%
Real estate loans | Commercial non-owner occupied
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	1,668	1,337	$ 1,604	$ 1,266
Charge-offs	(488)	0	(488)	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	585	113	649	184
Balance, at the end of the period	1,765	1,450	1,765	1,450
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	1,765	1,450	1,765	1,450
Loans individually evaluated for impairment	243	1,290	$ 243	$ 1,290
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	2,121,069	1,218,457	$ 2,121,069	$ 1,218,457
General reserves to total loans collectively evaluated for impairment			0.08%	0.12%
Gross loans, excluding loan receivable held for sale	2,121,312	1,219,747	$ 2,121,312	$ 1,219,747
Total allowance to gross loans			0.08%	0.12%
Real estate loans | Multi-family
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	669	592	$ 725	$ 607
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	36	(29)	(20)	(44)
Balance, at the end of the period	705	563	705	563
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	705	563	705	563
Loans individually evaluated for impairment	0	589	$ 0	$ 589
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	1,520,135	804,905	$ 1,520,135	$ 804,905
General reserves to total loans collectively evaluated for impairment			0.05%	0.07%
Gross loans, excluding loan receivable held for sale	1,520,135	805,494	$ 1,520,135	$ 805,494
Total allowance to gross loans			0.05%	0.07%
Real estate loans | One-to-four family
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	758	745	$ 805	$ 803
Charge-offs	0	0	0	0
Recoveries	1	1	1	1
Provisions for (reduction in) loan losses	(55)	(48)	(102)	(106)
Balance, at the end of the period	704	698	704	698
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	$ 0
Amount of allowance attributed to: General portfolio allocation	704	698	704	698
Loans individually evaluated for impairment	380	1,445	$ 380	$ 1,445
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	248,012	248,050	$ 248,012	$ 248,050
General reserves to total loans collectively evaluated for impairment			0.28%	0.28%
Gross loans, excluding loan receivable held for sale	248,392	249,495	$ 248,392	$ 249,495
Total allowance to gross loans			0.28%	0.28%
Real estate loans | Construction
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	5,194	5,075	$ 5,166	$ 4,569
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	(444)	(266)	(416)	240
Balance, at the end of the period	4,750	4,809	4,750	4,809
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	4,750	4,809	4,750	4,809
Loans individually evaluated for impairment	0	0	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	505,401	321,423	$ 505,401	$ 321,423
General reserves to total loans collectively evaluated for impairment			0.94%	1.50%
Gross loans, excluding loan receivable held for sale	505,401	321,423	$ 505,401	$ 321,423
Total allowance to gross loans			0.94%	1.50%
Real estate loans | Farmland
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	664	234	$ 503	$ 137
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	145	171	306	268
Balance, at the end of the period	809	405	809	405
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	809	405	809	405
Loans individually evaluated for impairment	0	0	$ 0	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	169,724	136,548	$ 169,724	$ 136,548
General reserves to total loans collectively evaluated for impairment			0.48%	0.30%
Gross loans, excluding loan receivable held for sale	169,724	136,548	$ 169,724	$ 136,548
Total allowance to gross loans			0.48%	0.30%
Real estate loans | Land
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	766	1,172	$ 772	$ 993
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	(108)	(200)	(114)	(21)
Balance, at the end of the period	658	972	658	972
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	658	972	658	972
Loans individually evaluated for impairment	480	6	$ 480	$ 6
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	40,268	30,240	$ 40,268	$ 30,240
General reserves to total loans collectively evaluated for impairment			1.63%	3.21%
Gross loans, excluding loan receivable held for sale	40,748	30,246	$ 40,748	$ 30,246
Total allowance to gross loans			1.61%	3.21%
Consumer Loans | Consumer loans
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	201	50	$ 219	$ 95
Charge-offs	0	0	(5)	(52)
Recoveries	0	1	1	1
Provisions for (reduction in) loan losses	20	48	6	55
Balance, at the end of the period	221	99	221	99
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	221	99	221	99
Loans individually evaluated for impairment	0	15	$ 0	$ 15
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	40,680	81,958	$ 40,680	$ 81,958
General reserves to total loans collectively evaluated for impairment			0.54%	0.12%
Gross loans, excluding loan receivable held for sale	$ 40,680	$ 81,973	$ 40,680	$ 81,973
Total allowance to gross loans			0.54%	0.12%
Owner Occupied Commercial Real Estate Loans Commercial And Industrial Loans And Small Business Administration Loans
Allowance for Loan Losses
Period considered for comparison of allowance for loan losses factor (in years)			1 year
Period considered for comparison of entity's allowance for loan losses factor (in years)			1 year 7 months 6 days