Quarterly Financial Information (Unaudited) (Restatement Amounts for Discontinued Operations Adjustment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Data [Abstract]
Revenues	$ 732,856	[1]	$ 710,924	[1]	$ 683,764	[1]	$ 682,509	[1]	$ 655,730	[2]	$ 637,218	[2]	$ 610,188	[2]	$ 564,597	[2]	$ 2,810,053	$ 2,467,733	$ 1,731,704
Income from continuing operations attributable to common stockholders	108,338	[1]	127,268	[1]	132,895	[1]	120,429	[1]	101,439	[2]	115,737	[2]	43,413	[2]	47,246	[2]	488,930	307,835	362,308
Discontinued operations	102	[1]	(8,972)	[1]	(18,315)	[1]	(8,236)	[1]	(15,172)	[2]	(3,855)	[2]	30,612	[2]	43,380	[2]	(35,421)	54,965	2,185
Previously Reported
Quarterly Financial Data [Abstract]
Revenues			712,386		685,846		684,868		660,711		641,520		614,502		568,566
Income from continuing operations attributable to common stockholders			127,380		132,635		117,820		97,992		115,975		43,496		48,110
Discontinued operations			(9,084)		(18,055)		(5,627)		(11,725)		(4,093)		30,529		42,516
Restatement Adjustment
Quarterly Financial Data [Abstract]
Revenues			(1,462)		(2,082)		(2,359)		(4,981)		(4,302)		(4,314)		(3,969)
Income from continuing operations attributable to common stockholders			(112)		260		2,609		3,447		(238)		(83)		(864)
Discontinued operations			$ 112		$ (260)		$ (2,609)		$ (3,447)		$ 238		$ 83		$ 864

[1] The amounts presented for the three months ended March 31, 2013, June 30, 2013 and September 30, 2013 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 2013 or classified as held for sale as of December 31, 2013.

[2] The amounts presented for the three months ended March 31, 2012, June 30, 2012, September 30, 2012 and December 31, 2012 differ from the amounts previously reported in our Annual Report on Form 10-K for the year ended December 31, 2012 as a result of discontinued operations consisting of properties sold in 2013 or classified as held for sale as of December 31, 2013.