Quarterly Results of Operations (Tables)

12 Months Ended

Dec. 31, 2012

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

	QUARTER ENDED
	DEC. 31,	SEPT. 30,		JUNE 30,	MAR. 31,	DEC. 31,	SEPT. 30,	JUNE 30,	MAR. 31,
	2012	2012		2012	2012	2011	2011	2011 (2)	2011
Operating revenue	$176,227	$171,727		$168,567	$169,031	$168,704	$165,192	$163,948	$165,397
Income from continuing operations	32,178	31,742		34,460	35,450	34,387	35,889	38,987	30,798
Discontinued operations	8,392	(1,845	)	3,221	4,153	6,858	5,792	53,854	4,145
Net income	40,570	29,897		37,681	39,603	41,245	41,681	92,841	34,943
Income per common share - basic (1)	0.33	0.24		0.29	0.32	0.30	0.31	0.74	0.25
Income per common share - diluted (1)	0.32	0.24		0.29	0.32	0.30	0.31	0.74	0.25

(1) The sum of quarterly financial data may vary from the annual data due to rounding.

(2) Includes gain on sale included in discontinued operations of $50.2 million.