Loans, Allowance for Loan Losses, and Credit Quality - Summary of loan composition (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 2,242,931	$ 2,166,181
Less allowance for loan losses (“ALLL”)	13,620	13,153	$ 12,992	$ 12,653
Loans, net	$ 2,229,311	$ 2,153,028
Percent of total	100.00%	100.00%
Allowance for loan losses to loans	0.61%	0.61%
Percentage of loans originated	74.00%	69.00%
Percentage of loans acquired	26.00%	31.00%
Retail & other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 28,713	$ 26,493
Less allowance for loan losses (“ALLL”)	314	304		225
Loans, net	$ 28,399	$ 26,189
Percent of total	1.00%	1.00%
Commercial portfolio segment | Commercial & industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 763,742	$ 684,920
Less allowance for loan losses (“ALLL”)	5,658	5,271		4,934
Loans, net	$ 758,084	$ 679,649
Percent of total	34.00%	32.00%
Commercial portfolio segment | Owner-occupied CRE
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 456,508	$ 441,353
Less allowance for loan losses (“ALLL”)	2,779	2,847		2,607
Loans, net	$ 453,729	$ 438,506
Percent of total	20.00%	20.00%
Commercial portfolio segment | AG production
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 36,050	$ 35,625
Less allowance for loan losses (“ALLL”)	206	121		129
Loans, net	$ 35,844	$ 35,504
Percent of total	2.00%	2.00%
Commercial real estate portfolio segment | AG real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 58,591	$ 53,444
Less allowance for loan losses (“ALLL”)	347	301		296
Loans, net	$ 58,244	$ 53,143
Percent of total	3.00%	2.00%
Commercial real estate portfolio segment | CRE investment
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 336,442	$ 343,652
Less allowance for loan losses (“ALLL”)	1,502	1,470		1,388
Loans, net	$ 334,940	$ 342,182
Percent of total	15.00%	16.00%
Commercial real estate portfolio segment | Construction & land development
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 61,810	$ 80,599
Less allowance for loan losses (“ALLL”)	370	510		726
Loans, net	$ 61,440	$ 80,089
Percent of total	3.00%	4.00%
Residential | Residential construction
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 41,496	$ 30,926
Less allowance for loan losses (“ALLL”)	342	211		251
Loans, net	$ 41,154	$ 30,715
Percent of total	2.00%	1.00%
Residential | Residential first mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 343,400	$ 357,841
Less allowance for loan losses (“ALLL”)	1,607	1,646		1,609
Loans, net	$ 341,793	$ 356,195
Percent of total	15.00%	17.00%
Residential | Residential junior mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 116,179	$ 111,328
Less allowance for loan losses (“ALLL”)	495	472		488
Loans, net	$ 115,684	$ 110,856
Percent of total	5.00%	5.00%
Originated
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 1,650,693	$ 1,485,165
Less allowance for loan losses (“ALLL”)	12,064	11,448		10,542
Loans, net	$ 1,638,629	$ 1,473,717
Percent of total	100.00%	100.00%
Allowance for loan losses to loans	0.73%	0.77%
Originated | Retail & other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 27,232	$ 23,809
Less allowance for loan losses (“ALLL”)	293	281		200
Loans, net	$ 26,939	$ 23,528
Percent of total	2.00%	2.00%
Originated | Commercial portfolio segment | Commercial & industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 660,040	$ 568,100
Less allowance for loan losses (“ALLL”)	5,109	4,683		4,192
Loans, net	$ 654,931	$ 563,417
Percent of total	40.00%	38.00%
Originated | Commercial portfolio segment | Owner-occupied CRE
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 321,323	$ 283,531
Less allowance for loan losses (“ALLL”)	2,411	2,439		2,115
Loans, net	$ 318,912	$ 281,092
Percent of total	19.00%	19.00%
Originated | Commercial portfolio segment | AG production
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 11,450	$ 11,113
Less allowance for loan losses (“ALLL”)	194	110		112
Loans, net	$ 11,256	$ 11,003
Percent of total	1.00%	1.00%
Originated | Commercial real estate portfolio segment | AG real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 38,616	$ 31,374
Less allowance for loan losses (“ALLL”)	300	255		235
Loans, net	$ 38,316	$ 31,119
Percent of total	2.00%	2.00%
Originated | Commercial real estate portfolio segment | CRE investment
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 180,427	$ 171,087
Less allowance for loan losses (“ALLL”)	1,298	1,230		1,154
Loans, net	$ 179,129	$ 169,857
Percent of total	11.00%	12.00%
Originated | Commercial real estate portfolio segment | Construction & land development
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 52,806	$ 66,478
Less allowance for loan losses (“ALLL”)	320	431		628
Loans, net	$ 52,486	$ 66,047
Percent of total	3.00%	4.00%
Originated | Residential | Residential construction
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 41,246	$ 30,926
Less allowance for loan losses (“ALLL”)	308	211		200
Loans, net	$ 40,938	$ 30,715
Percent of total	3.00%	2.00%
Originated | Residential | Residential first mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 228,312	$ 220,368
Less allowance for loan losses (“ALLL”)	1,394	1,400		1,297
Loans, net	$ 226,918	$ 218,968
Percent of total	14.00%	15.00%
Originated | Residential | Residential junior mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 89,241	$ 78,379
Less allowance for loan losses (“ALLL”)	437	408		409
Loans, net	$ 88,804	$ 77,971
Percent of total	5.00%	5.00%
Acquired
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 592,238	$ 681,016
Less allowance for loan losses (“ALLL”)	1,556	1,705		2,111
Loans, net	$ 590,682	$ 679,311
Percent of total	100.00%	100.00%
Allowance for loan losses to loans	0.26%	0.25%
Acquired | Retail & other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 1,481	$ 2,684
Less allowance for loan losses (“ALLL”)	21	23		25
Loans, net	$ 1,460	$ 2,661
Percent of total	0.00%	1.00%
Acquired | Commercial portfolio segment | Commercial & industrial
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 103,702	$ 116,820
Less allowance for loan losses (“ALLL”)	549	588		742
Loans, net	$ 103,153	$ 116,232
Percent of total	18.00%	17.00%
Acquired | Commercial portfolio segment | Owner-occupied CRE
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 135,185	$ 157,822
Less allowance for loan losses (“ALLL”)	368	408		492
Loans, net	$ 134,817	$ 157,414
Percent of total	23.00%	23.00%
Acquired | Commercial portfolio segment | AG production
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 24,600	$ 24,512
Less allowance for loan losses (“ALLL”)	12	11		17
Loans, net	$ 24,588	$ 24,501
Percent of total	4.00%	4.00%
Acquired | Commercial real estate portfolio segment | AG real estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 19,975	$ 22,070
Less allowance for loan losses (“ALLL”)	47	46		61
Loans, net	$ 19,928	$ 22,024
Percent of total	3.00%	3.00%
Acquired | Commercial real estate portfolio segment | CRE investment
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 156,015	$ 172,565
Less allowance for loan losses (“ALLL”)	204	240		234
Loans, net	$ 155,811	$ 172,325
Percent of total	26.00%	25.00%
Acquired | Commercial real estate portfolio segment | Construction & land development
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 9,004	$ 14,121
Less allowance for loan losses (“ALLL”)	50	79		98
Loans, net	$ 8,954	$ 14,042
Percent of total	2.00%	2.00%
Acquired | Residential | Residential construction
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 250	$ 0
Less allowance for loan losses (“ALLL”)	34	0		51
Loans, net	$ 216	$ 0
Percent of total	0.00%	0.00%
Acquired | Residential | Residential first mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 115,088	$ 137,473
Less allowance for loan losses (“ALLL”)	213	246		312
Loans, net	$ 114,875	$ 137,227
Percent of total	19.00%	20.00%
Acquired | Residential | Residential junior mortgage
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 26,938	$ 32,949
Less allowance for loan losses (“ALLL”)	58	64		$ 79
Loans, net	$ 26,880	$ 32,885
Percent of total	5.00%	5.00%