Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Segment Information
Rental income	$ 275,048	$ 243,378
Operating expenses	(109,659)	(97,236)
Property net operating income (NOI)	165,389	146,142
Reconciliation of NOI to net income
Property NOI	165,389	146,142
Depreciation and amortization	(66,523)	(58,019)
General and administrative	(17,266)	(11,536)
Acquisition related costs	(628)	(2,502)
Operating income	80,972	74,085
Interest and other income	458	285
Interest expense	(52,344)	(49,106)
Loss on early extinguishment of debt	(60,027)	(67)
Equity in earnings of investees	4,262	2,958
Gain on sale of equity investment	66,293
Income from continuing operations before income tax expense	39,614	28,155
Income tax expense	(988)	(492)
Income from continuing operations	38,626	27,663
Loss from discontinued operations	(1,912)	(3,089)
Loss on asset impairment from discontinued operations	(3,946)
Gain on sale of properties from discontinued operations	1,260
Income before gain on sale of properties	34,028	24,574
Gain on sale of properties	1,596
Net income	$ 35,624	$ 24,574

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 23

-URI http://asc.fasb.org/extlink&oid=21917927&loc=d3e1043-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 59

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.