Statements of Common Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2017	$ 79,201	$ 40,204	$ 119,405
Balance (in shares) at Dec. 31, 2017	12,872,742
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	5,899	5,899
Dividends	0	(4,296)	(4,296)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 1,146	0	1,146
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	37,782
Stock-based compensation	$ 57	0	57
Stock-based compensation (in shares)	3,743
Balance at Jun. 30, 2018	$ 80,404	41,807	122,211
Balance (in shares) at Jun. 30, 2018	12,914,267
Balance at Mar. 31, 2018	$ 79,796	40,652	120,448
Balance (in shares) at Mar. 31, 2018	12,892,798
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	3,305	3,305
Dividends	0	(2,150)	(2,150)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 555	0	555
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	17,726
Stock-based compensation	$ 53	0	53
Stock-based compensation (in shares)	3,743
Balance at Jun. 30, 2018	$ 80,404	41,807	122,211
Balance (in shares) at Jun. 30, 2018	12,914,267
Balance at Dec. 31, 2018	$ 81,305	44,890	$ 126,195
Balance (in shares) at Dec. 31, 2018	12,943,536		12,943,536
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	6,530	$ 6,530
Dividends	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		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
Dividends	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		12,974,287