Statements of Common Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2009	$ 73,569	$ 13,353	$ 86,922
Balance (in shares) at Dec. 31, 2009	12,558,724
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	8,929	8,929
Dividends	0	(6,506)	(6,506)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	1,912	0	1,912
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	133,330
Balance at Dec. 31, 2010	75,481	15,776	91,257
Balance (in shares) at Dec. 31, 2010	12,692,054
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	9,084	9,084
Dividends	0	(6,708)	(6,708)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	1,632	0	1,632
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	99,617
Balance at Dec. 31, 2011	77,113	18,152	95,265
Balance (in shares) at Dec. 31, 2011	12,791,671		12,791,671
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	9,303	9,303
Dividends	0	(6,929)	(6,929)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	2,186	0	2,186
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	126,962
Balance at Dec. 31, 2012	$ 79,299	$ 20,526	$ 99,825
Balance (in shares) at Dec. 31, 2012	12,918,633		12,918,633