Quarterly Financial Information (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
Quarterly Financial Data [Abstract]
Revenues, previously reported in Form 10-Q			$ 641,950		$ 616,448		$ 573,694		$ 571,401		$ 562,528		$ 362,630		$ 268,432
Revenues, previously reported, subsequently reclassified to discontinued operations in Form 10-Q			430		1,946		5,128		8,256		7,837		3,209		2,036
Total revenues disclosed in Form 10-K	660,711	[1]	641,520	[1]	614,502	[1]	568,566	[1]	563,145	[2]	554,691	[2]	359,421	[2]	266,396	[2]	2,485,299	1,743,653	1,000,634
Income from continuing operations attributable to common stockholders, previously reported in Form 10-Q			115,329		42,543		48,297		193,216		102,470		18,906		48,218
Income from continuing operations attributable to common stockholders, previously reported in Form 10-Q subsequently reclassified to discontinued operations			(646)		(953)		187		(337)		(721)		456		279
Income from continuing operations attributable to common stockholders	97,992	[1]	115,975	[1]	43,496	[1]	48,110	[1]	193,553	[2]	103,191	[2]	18,450	[2]	47,939	[2]	305,573	363,133	213,444
Discontinued operations, previously reported in Form 10-Q			(3,447)		31,482		42,329		(268)		415		770		766
Discontinued operations from properties sold or held for sale subsequent to the respective reporting period			(646)		(953)		187		(337)		(721)		456		279
Discontinued operations disclosed in Form 10-K	$ (11,725)	[1]	$ (4,093)	[1]	$ 30,529	[1]	$ 42,516	[1]	$ (605)	[2]	$ (306)	[2]	$ 1,226	[2]	$ 1,045	[2]	$ 57,227	$ 1,360	$ 32,723

[1] The amounts presented for the three months ended March 31, 2012, June 30, 2012 and September 30, 2012 differ from the amounts previously reported in our Quarterly Reports on Form 10-Q as a result of discontinued operations consisting of properties sold in 2012 or classified as held for sale as of December 31, 2012.

[2] The amounts presented for the three months ended March 31, 2011, June 30, 2011, September 30, 2011 and December 31, 2011 differ from the amounts previously reported in our Annual Report on Form 10-K for the year ended December 31, 2011 as a result of discontinued operations consisting of properties sold in 2012 or classified as held for sale as of December 31, 2012.