Selected Quarterly Financial Data (Unaudited) (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Total revenues	$ 264,692	$ 255,225	$ 249,797	$ 243,378	$ 233,528	$ 232,282	$ 208,883	$ 199,539	$ 1,013,092	$ 874,232	$ 720,747
Previously reported
Total revenues		261,661	255,374	251,246	241,552	241,785	217,938	210,673
Total revenues from properties reclassified (to) from discontinued operations during 2012
Revenues from properties reclassified (to) from discontinued operations		$ (6,436)	$ (5,577)	$ (7,868)	$ (8,024)	$ (9,503)	$ (9,055)	$ (11,134)