Statements of Common Stockholders' Equity (Unaudited) (USD $) In Thousands, except Share data	Common Stock [Member]	Retained Earnings [Member]	Total
Balance at Dec. 31, 2011	$ 77,113	$ 18,152	$ 95,265
Balance (in shares) at Dec. 31, 2011	12,791,671
Net income	0	6,905	6,905
Dividends	0	(5,145)	(5,145)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	1,634	0	1,634
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	94,611
Balance at Sep. 30, 2012	78,747	19,912	98,659
Balance (in shares) at Sep. 30, 2012	12,886,282
Balance at Dec. 31, 2012	79,299	20,526	99,825
Balance (in shares) at Dec. 31, 2012	12,918,633		12,918,633
Net income	0	7,016	7,016
Dividends	0	(5,359)	(5,359)
Retirement of common stock	(1,772)	0	(1,772)
Retirement of common stock (in shares)	(94,414)		(94,414)
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans	2,075	0	2,075
Issuance of common stock under dividend reinvestment, direct stock and employee stock purchase plans (in shares)	109,476
Balance at Sep. 30, 2013	$ 79,602	$ 22,183	$ 101,785
Balance (in shares) at Sep. 30, 2013	12,933,695		12,933,695