Condensed Financial Information of Parent (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	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 14,433	$ 21,418	$ 16,918	$ 15,270	$ 19,134	$ 21,649	$ 21,056	$ 16,559	$ 14,433	$ 19,134
Premises and equipment	21,305				22,056				21,305	22,056
Goodwill	29,805				29,805				29,805	29,805
Other assets	47,799				42,536				47,799	42,536
Total assets	2,068,796	2,033,227	1,998,699	1,991,345	1,944,570	1,981,854	1,913,961	1,871,815	2,068,796	1,944,570
Liabilities and shareholders' equity
Other liabilities	20,867	20,031	19,292	16,264	15,626	17,008	16,556	18,022	20,867	15,626
Total liabilities	1,856,288				1,753,028				1,856,288	1,753,028
Shareholders' equity
Common stock	109				109				109	109
Additional paid-in capital	63,964				62,746				63,964	62,746
Retained earnings	144,839				132,460				144,839	132,460
Total shareholders' equity	212,508	208,489	204,593	197,787	191,542	184,661	183,304	181,372	212,508	191,542	$ 181,321	$ 172,521
Total liabilities and shareholders' equity	2,068,796	2,033,227	1,998,699	1,991,345	1,944,570	1,981,854	1,913,961	1,871,815	2,068,796	1,944,570
Statements of Income
Net securities gains (losses)									224	137	471
Income before income taxes	7,947	7,468	7,575	7,270	7,585	7,021	6,774	6,462	30,260	27,842	26,200
Applicable tax expense	1,261	1,180	1,180	1,114	1,222	1,088	1,040	956	4,735	4,306	6,612
Equity in earnings of Bank
Net income	6,686	6,288	6,395	6,156	6,363	5,933	5,734	5,506	25,525	23,536	19,588
Cash flows from operating activities
Net income	6,686	$ 6,288	$ 6,395	6,156	6,363	$ 5,933	$ 5,734	5,506	25,525	23,536	19,588
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation									1,938	1,792	1,864
Equity compensation expense									565	381	392
(Gain) loss on sale of investments									(224)	(137)	(471)
(Increase) decrease in other assets									(7,690)	1,146	(4,817)
Decrease in other liabilities									2,802	3,848	(2,020)
Net cash provided by operating activities									26,053	33,840	22,273
Cash flows from investing activities
Proceeds from maturities, payments, calls of securities available for sale									78,825	51,752	156,969
Capital expenditures									(1,573)	(1,484)	(2,529)
Net cash used in investing activities									(116,280)	(112,077)	(130,060)
Cash flows from financing activities
Purchase of common stock									(183)	(168)	(154)
Proceeds from sale of common stock									653	619	632
Dividends paid									(12,963)	(12,052)	(11,460)
Net cash provided by financing activities									85,526	78,164	109,628
Cash and cash equivalents at beginning of year				19,134				19,207	19,134	19,207	17,366
Cash and cash equivalents at end of year	14,433				19,134				14,433	19,134	19,207
Parent Company
Assets
Cash and cash equivalents	1,028				1,190				1,028	1,190
Dividends receivable	3,200				2,950				3,200	2,950
Investment in subsidiary	183,654				162,763				183,654	162,763
Premises and equipment	0				2				0	2
Goodwill	27,559				27,559				27,559	27,559
Other assets	337				232				337	232
Total assets	215,778				194,696				215,778	194,696
Liabilities and shareholders' equity
Dividends payable	3,270				3,150				3,270	3,150
Other liabilities	0				4				0	4
Total liabilities	3,270				3,154				3,270	3,154
Shareholders' equity
Common stock	109				109				109	109
Additional paid-in capital	63,964				62,746				63,964	62,746
Retained earnings	148,435				128,687				148,435	128,687
Total shareholders' equity	212,508				191,542				212,508	191,542
Total liabilities and shareholders' equity	215,778				194,696				215,778	194,696
Statements of Income
Interest and dividends on investments									0	0	15
Net securities gains (losses)									0	137	(3)
Total income									0	137	12
Occupancy expense									1	2	5
Other operating expense									826	652	588
Total expense									827	654	593
Income before income taxes									(827)	(517)	(581)
Applicable tax expense									(230)	(164)	(187)
Loss before Bank earnings									(597)	(353)	(394)
Equity in earnings of Bank
Remitted									12,600	11,300	11,180
Unremitted									13,522	12,589	8,802
Net income									25,525	23,536	19,588
Cash flows from operating activities
Net income									25,525	23,536	19,588
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation									2	0	5
Equity compensation expense									565	381	392
(Gain) loss on sale of investments									0	(137)	3
(Increase) decrease in other assets									(105)	81	27
(Increase) decrease in dividends receivable									(250)	(450)	1,300
Increase (decrease) in dividends payable									120	551	(1,179)
Decrease in other liabilities									(4)	0	(3)
Unremitted earnings of Bank									(13,522)	(12,589)	(8,802)
Net cash provided by operating activities									12,331	11,373	11,331
Cash flows from investing activities
Proceeds from maturities, payments, calls of securities available for sale									0	459	0
Capital expenditures									0	1	(4)
Net cash used in investing activities									0	460	(4)
Cash flows from financing activities
Purchase of common stock									(183)	(168)	(154)
Proceeds from sale of common stock									653	619	632
Dividends paid									(12,963)	(12,052)	(11,460)
Net cash provided by financing activities									(12,493)	(11,601)	(10,982)
Net increase (decrease) in cash and cash equivalents									(162)	232	345
Cash and cash equivalents at beginning of year				$ 1,190				$ 958	1,190	958	613
Cash and cash equivalents at end of year	$ 1,028				$ 1,190				$ 1,028	$ 1,190	$ 958