Acquisitions (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 01, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Merger related expense		$ 0	$ 0	$ 11,322	$ 0
Consideration Paid:
Issuance of common stock (in shares)	2,361,686	2,361,686		2,361,686
Cash paid in lieu of fractional shares				$ 27	0
Liabilities assumed:
Long-term FHLB advances	$ 778
Goodwill		$ 84,633	43,872	84,633	43,872	$ 43,872	[1]
Interest component of expected cash flows (accretable yield)				4,410		$ 0
HomeTown Bankshares Corporation Merger
Business Acquisition [Line Items]
Number of shares issued per share of common stock (in shares)	0.4150
Consideration Paid:
Issuance of common shares, replacement options, and restricted stock	$ 753
Cash paid in lieu of fractional shares	27
Value of consideration	83,250
Assets acquired:
Cash and cash equivalents	26,283
Investment securities	34,876
Restricted stock	2,588
Loans	444,324
Premises and equipment	12,554
Deferred income taxes	2,329
Core deposit intangible	8,200
Other real estate owned	1,442
Banked owned life insurance	8,246
Other assets	14,244
Total assets	555,086
Liabilities assumed:
Deposits	483,626
Short-term FHLB advances	14,883
Subordinated debt	7,530
Other liabilities	5,780
Total liabilities	512,597
Net assets acquired	42,489
Goodwill	40,761
Contractually required principal and interest at acquisition	45,551
Contractual cash flows not expected to be collected (nonaccretable difference)	8,296
Expected cash flows at acquisition	37,255
Interest component of expected cash flows (accretable yield)	4,410
Fair value of acquired loans accounted for under FASB ASC 310-30	32,845
Business Acquisition, Pro Forma Information [Abstract]
Total revenues		24,636	24,478	70,404	73,897
Net income		$ 8,608	$ 7,458	$ 21,996	$ 22,213
Earnings per share (in dollars per share)		$ 0.77	$ 0.67	$ 1.98	$ 2.01
Acquisition-related Costs | HomeTown Bankshares Corporation Merger
Business Acquisition [Line Items]
Merger related expense				$ 11,300
Data Processing Termination and Conversion Costs | HomeTown Bankshares Corporation Merger
Business Acquisition [Line Items]
Merger related expense				9,100
Legal and Professional Fees | HomeTown Bankshares Corporation Merger
Business Acquisition [Line Items]
Merger related expense				1,700
Salary and Related Expense | HomeTown Bankshares Corporation Merger
Business Acquisition [Line Items]
Merger related expense				400
Other Noninterest Expense | HomeTown Bankshares Corporation Merger
Business Acquisition [Line Items]
Merger related expense				$ 100
Common Stock | HomeTown Bankshares Corporation Merger
Consideration Paid:
Issuance of common shares, replacement options, and restricted stock	$ 82,470

[1] Derived from audited consolidated financial statements.