Statements of Common Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2016	$ 78,513	$ 35,548	$ 0	$ 114,061
Balance (in shares) at Dec. 31, 2016	12,852,295
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	2,581	0	2,581
Dividends	$ 0	(2,060)	0	$ (2,060)
Repurchase of common stock (in shares)	(24,329)			(24,329)
Repurchase of common stock	$ 0	0	(825)	$ (825)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 522	0	0	522
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	15,084
Stock-based compensation	$ 2	0	0	2
Stock-based compensation (in shares)	0
Balance at Mar. 31, 2017	$ 79,037	36,069	(825)	114,281
Balance (in shares) at Mar. 31, 2017	12,843,050
Balance at Dec. 31, 2017	$ 79,201	40,204	0	$ 119,405
Balance (in shares) at Dec. 31, 2017	12,872,742			12,872,742
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 0	2,594	0	$ 2,594
Dividends	0	(2,146)	0	$ (2,146)
Repurchase of common stock (in shares)				0
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	$ 591	0	0	$ 591
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	20,056
Stock-based compensation	$ 4	0	0	4
Stock-based compensation (in shares)	0
Balance at Mar. 31, 2018	$ 79,796	$ 40,652	$ 0	$ 120,448
Balance (in shares) at Mar. 31, 2018	12,892,798			12,892,798