Statements of Common Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2018	$ 81,305	$ 44,890	$ 126,195
Balance (in shares) at Dec. 31, 2018	12,943,536
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	6,530	6,530
Cash dividends declared	0	(4,489)	(4,489)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 799	0	799
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	23,788
Stock-based compensation	$ 79	0	79
Stock-based compensation (in shares)	6,963
Balance at Jun. 30, 2019	$ 82,183	46,931	129,114
Balance (in shares) at Jun. 30, 2019	12,974,287
Balance at Mar. 31, 2019	$ 81,703	45,460	127,163
Balance (in shares) at Mar. 31, 2019	12,954,976
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	3,717	3,717
Cash dividends declared	0	(2,246)	(2,246)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 415	0	415
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	12,348
Stock-based compensation	$ 65	0	65
Stock-based compensation (in shares)	6,963
Balance at Jun. 30, 2019	$ 82,183	46,931	129,114
Balance (in shares) at Jun. 30, 2019	12,974,287
Balance at Dec. 31, 2019	$ 83,976	50,209	$ 134,185
Balance (in shares) at Dec. 31, 2019	13,014,898		13,014,898
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	8,184	$ 8,184
Cash dividends declared	0	(4,693)	(4,693)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 844	0	844
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	19,101
Stock-based compensation	$ 52	0	52
Stock-based compensation (in shares)	0
Balance at Jun. 30, 2020	$ 84,872	53,700	$ 138,572
Balance (in shares) at Jun. 30, 2020	13,033,999		13,033,999
Balance at Mar. 31, 2020	$ 84,424	51,865	$ 136,289
Balance (in shares) at Mar. 31, 2020	13,024,187
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	4,182	4,182
Cash dividends declared	0	(2,347)	(2,347)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 433	0	433
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	9,812
Stock-based compensation	$ 15	0	15
Stock-based compensation (in shares)	0
Balance at Jun. 30, 2020	$ 84,872	$ 53,700	$ 138,572
Balance (in shares) at Jun. 30, 2020	13,033,999		13,033,999