Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	$ 30,502	$ 23,075	$ 28,936	$ 21,296
Charge-offs	(273)	(110)	(1,019)	(870)
Recoveries	165	186	224	223
Provisions for (reduction in) loan losses	1,353	1,904	3,606	4,406
Balance, at the end of the period	31,747	25,055	31,747	25,055
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	$ 55
Amount of allowance attributed to: General portfolio allocation	31,747	25,055	31,747	25,055
Loans individually evaluated for impairment	6,039	395	$ 6,039	$ 395
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	6,274,810	4,857,648	$ 6,274,810	$ 4,857,648
General reserves to total loans collectively evaluated for impairment			0.51%	0.52%
Gross loans, excluding loan receivable held for sale	6,280,849	4,858,043	$ 6,280,849	$ 4,858,043
Total allowance to gross loans			0.51%	0.52%
Business loans | Commercial and industrial
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	9,492	6,949	$ 9,721	$ 6,362
Charge-offs	(246)	(110)	(911)	(862)
Recoveries	138	33	163	55
Provisions for (reduction in) loan losses	780	772	1,191	2,089
Balance, at the end of the period	10,164	7,644	10,164	7,644
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	10,164	7,644	10,164	7,644
Loans individually evaluated for impairment	1,062	0	$ 1,062	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	1,101,524	733,852	$ 1,101,524	$ 733,852
General reserves to total loans collectively evaluated for impairment			0.92%	1.04%
Gross loans, excluding loan receivable held for sale	1,102,586	733,852	$ 1,102,586	$ 733,852
Total allowance to gross loans			0.92%	1.04%
Business loans | Franchise
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	6,095	4,474	$ 5,797	$ 3,845
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	86	893	384	1,522
Balance, at the end of the period	6,181	5,367	6,181	5,367
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	6,181	5,367	6,181	5,367
Loans individually evaluated for impairment	209	0	$ 209	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	708,748	565,415	$ 708,748	$ 565,415
General reserves to total loans collectively evaluated for impairment			0.87%	0.95%
Gross loans, excluding loan receivable held for sale	708,957	565,415	$ 708,957	$ 565,415
Total allowance to gross loans			0.87%	0.95%
Business loans | Commercial owner occupied
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	791	1,232	$ 767	$ 1,193
Charge-offs	0	0	0	0
Recoveries	16	70	24	82
Provisions for (reduction in) loan losses	330	(630)	346	(603)
Balance, at the end of the period	1,137	672	1,137	672
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	55
Amount of allowance attributed to: General portfolio allocation	1,137	672	1,137	672
Loans individually evaluated for impairment	0	206	$ 0	$ 206
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	1,310,722	729,270	$ 1,310,722	$ 729,270
General reserves to total loans collectively evaluated for impairment			0.09%	0.09%
Gross loans, excluding loan receivable held for sale	1,310,722	729,476	$ 1,310,722	$ 729,476
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	2,814	1,145	$ 2,890	$ 1,039
Charge-offs	(27)	0	(56)	(8)
Recoveries	9	81	35	83
Provisions for (reduction in) loan losses	(221)	1,293	(294)	1,405
Balance, at the end of the period	2,575	2,519	2,575	2,519
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	2,575	2,519	2,575	2,519
Loans individually evaluated for impairment	1,423	73	$ 1,423	$ 73
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	175,273	101,311	$ 175,273	$ 101,311
General reserves to total loans collectively evaluated for impairment			1.47%	2.49%
Gross loans, excluding loan receivable held for sale	176,696	101,384	$ 176,696	$ 101,384
Total allowance to gross loans			1.46%	2.48%
Business loans | Agribusiness
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	2,105	0	$ 1,291	$ 0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	589	206	1,403	206
Balance, at the end of the period	2,694	206	2,694	206
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	2,694	206	2,694	206
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	136,962	98,842	$ 136,962	$ 98,842
General reserves to total loans collectively evaluated for impairment			1.97%	0.21%
Gross loans, excluding loan receivable held for sale	136,962	98,842	$ 136,962	$ 98,842
Total allowance to gross loans			1.97%	0.21%
Real estate loans | Commercial non-owner occupied
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	1,337	1,847	$ 1,266	$ 1,715
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	113	(643)	184	(511)
Balance, at the end of the period	1,450	1,204	1,450	1,204
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	1,450	1,204	1,450	1,204
Loans individually evaluated for impairment	1,290	0	$ 1,290	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	1,218,457	1,095,184	$ 1,218,457	$ 1,095,184
General reserves to total loans collectively evaluated for impairment			0.12%	0.11%
Gross loans, excluding loan receivable held for sale	1,219,747	1,095,184	$ 1,219,747	$ 1,095,184
Total allowance to gross loans			0.12%	0.11%
Real estate loans | Multi-family
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	592	2,803	$ 607	$ 2,927
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	(29)	(2,192)	(44)	(2,316)
Balance, at the end of the period	563	611	563	611
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	563	611	563	611
Loans individually evaluated for impairment	589	0	$ 589	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	804,905	746,547	$ 804,905	$ 746,547
General reserves to total loans collectively evaluated for impairment			0.07%	0.08%
Gross loans, excluding loan receivable held for sale	805,494	746,547	$ 805,494	$ 746,547
Total allowance to gross loans			0.07%	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	745	373	$ 803	$ 365
Charge-offs	0	0	0	0
Recoveries	1	1	1	2
Provisions for (reduction in) loan losses	(48)	350	(106)	357
Balance, at the end of the period	698	724	698	724
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	698	724	698	724
Loans individually evaluated for impairment	1,445	104	$ 1,445	$ 104
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	248,050	321,944	$ 248,050	$ 321,944
General reserves to total loans collectively evaluated for impairment			0.28%	0.22%
Gross loans, excluding loan receivable held for sale	249,495	322,048	$ 249,495	$ 322,048
Total allowance to gross loans			0.28%	0.22%
Real estate loans | Construction
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	5,075	4,027	$ 4,569	$ 3,632
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	(266)	1,009	240	1,404
Balance, at the end of the period	4,809	5,036	4,809	5,036
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	4,809	5,036	4,809	5,036
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	321,423	289,600	$ 321,423	$ 289,600
General reserves to total loans collectively evaluated for impairment			1.50%	1.74%
Gross loans, excluding loan receivable held for sale	321,423	289,600	$ 321,423	$ 289,600
Total allowance to gross loans			1.50%	1.74%
Real estate loans | Farmland
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	234	0	$ 137	$ 0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	171	28	268	28
Balance, at the end of the period	405	28	405	28
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	405	28	405	28
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	136,548	136,587	$ 136,548	$ 136,587
General reserves to total loans collectively evaluated for impairment			0.30%	0.02%
Gross loans, excluding loan receivable held for sale	136,548	136,587	$ 136,548	$ 136,587
Total allowance to gross loans			0.30%	0.02%
Real estate loans | Land
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	1,172	204	$ 993	$ 198
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions for (reduction in) loan losses	(200)	755	(21)	761
Balance, at the end of the period	972	959	972	959
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0	$ 0
Amount of allowance attributed to: General portfolio allocation	972	959	972	959
Loans individually evaluated for impairment	6	12	$ 6	$ 12
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	30,240	31,787	$ 30,240	$ 31,787
General reserves to total loans collectively evaluated for impairment			3.21%	3.02%
Gross loans, excluding loan receivable held for sale	30,246	31,799	$ 30,246	$ 31,799
Total allowance to gross loans			3.21%	3.02%
Consumer Loans | Consumer loans
Allocation of allowance as well as the activity in allowance
Balance, at the beginning of the period	50	21	$ 95	$ 20
Charge-offs	0	0	(52)	0
Recoveries	1	1	1	1
Provisions for (reduction in) loan losses	48	63	55	64
Balance, at the end of the period	99	85	99	85
Other disclosures
Amount of allowance attributed to: Specifically evaluated impaired loans	0	0	0	0
Amount of allowance attributed to: General portfolio allocation	99	85	99	85
Loans individually evaluated for impairment	15	0	$ 15	$ 0
Specific reserves to total loans individually evaluated for impairment			0.00%	0.00%
Loans collectively evaluated for impairment	81,958	7,309	$ 81,958	$ 7,309
General reserves to total loans collectively evaluated for impairment			0.12%	1.16%
Gross loans, excluding loan receivable held for sale	$ 81,973	$ 7,309	$ 81,973	$ 7,309
Total allowance to gross loans			0.12%	1.16%
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 4 months 24 days