Summary of Quarterly results (Tables)

12 Months Ended

Dec. 31, 2011

Summary of Quarterly Results [Abstract]

Summary of Quarterly Results (Unaudited) [Table Text Block]

					Net Income
					Attributable to		Income Per
					Common		Common Share(1)
	(Amounts in thousands, except per share amounts)		Revenues		Stockholders		Basic		Diluted
	2011
		December 31	$	64,607	$	20,634	$	4.04	$	4.04
		September 30		64,737		20,425		4.00		4.00
		June 30		62,036		20,157		3.95		3.95
		March 31		62,872		18,207		3.57		3.57
	2010
		December 31	$	62,250	$	17,891	$	3.50	$	3.50
		September 30		61,390		17,875		3.50		3.50
		June 30		59,166		15,549		3.05		3.05
		March 31		58,544		15,114		2.96		2.96
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(1)	The total for the year may differ from the sum of the quarters as a result of weighting.