Unaudited Quarterly Financial Data

12 Months Ended

Dec. 31, 2011

Unaudited Quarterly Financial Data [Abstract]

Quarterly Financial Information [Text Block]

Unaudited Quarterly Financial Data

Summarized quarterly financial data is as follows:

	2011 Quarter Ended
	March		June	September	December
Operating revenue	$	43,696	59,007	73,914	62,338
Operating income	5,601		13,784	18,486	16,520
Net income	610		5,451	8,215	6,602
Comprehensive income	599		5,479	7,988	6,727
Earnings per share:
—Basic	0.03		0.29	0.44	0.36
—Diluted	0.03		0.29	0.44	0.35
Market price range of stock:
—High	26.40		24.24	24.80	24.93
—Low	22.48		21.99	21.16	21.10
Dividend per share	0.17		0.17	0.17	0.17
	2010 Quarter Ended
	March		June	September	December
Operating revenue	$	40,411	54,128	70,347	50,752
Operating income	5,337		11,345	17,922	3,471
Net income	985		4,516	10,787	8,118
Comprehensive income	1,498		3,276	8,906	(102	)
Earnings per share:
—Basic	0.05		0.24	0.58	0.45
—Diluted	0.05		0.24	0.58	0.43
Market price range of stock:
—High	26.12		28.23	26.20	27.88
—Low	21.76		22.78	22.57	23.88
Dividend per share	0.17		0.17	0.17	0.17