Condensed Consolidated Statements of Equity (USD $) In Thousands, unless otherwise specified	Total USD ($)	Class A common stock	Common stock Class A common stock USD ($)	Common stock Class B common stock USD ($)	Additional paid-in capital USD ($)	Accumulated distributions in excess of earnings USD ($)	Accumulated other comprehensive income USD ($)	Total Shareholders' Equity USD ($)	Noncontrolling interests USD ($)
Balance at Dec. 31, 2010	$ 2,296,065		$ 47	$ 144	$ 4,383,567	$ (2,111,138)	$ 22,282	$ 2,294,902	$ 1,163
Balance (in shares) at Dec. 31, 2010			47,734	143,204
Increase (Decrease) in Shareholders' Equity
Net loss (excluding net income of $23 attributable to redeemable noncontrolling interests)	(58,772)					(58,772)		(58,772)
Distribution upon dissolution of partnership	(8,484)					(8,483)		(8,483)	(1)
Net unrealized (loss) gain on derivative instruments	971						971	971
Net unrealized gain (loss) on marketable securities	(3,843)						(3,843)	(3,843)
Reversal of unrealized gain to recognized gain on marketable securities	(277)						(277)	(277)
Contributions from noncontrolling interests	332								332
Distributions declared ($0.50 and $0.30 per weighted average number of common shares outstanding for the nine months ended September 30, 2012 and 2011, respectively)	(58,464)					(58,464)		(58,464)
Distribution reinvestment program (DRP)	32,754			2	32,752			32,754
Distribution reinvestment program (DRP) (in shares)			478	1,434
Issuance of restricted common stock (in shares)			4	10
Stock based compensation expense	87				87			87
Balance at Sep. 30, 2011	2,200,369		47	146	4,416,406	(2,236,857)	19,133	2,198,875	1,494
Balance (in shares) at Sep. 30, 2011			48,216	144,648
Balance at Dec. 31, 2011	2,136,518		48	146	4,427,977	(2,312,877)	19,730	2,135,024	1,494
Balance (in shares) at Dec. 31, 2011		48,382	48,382	145,147
Increase (Decrease) in Shareholders' Equity
Net loss (excluding net income of $23 attributable to redeemable noncontrolling interests)	(14,564)					(14,564)		(14,564)
Net unrealized (loss) gain on derivative instruments	(591)						(591)	(591)
Net unrealized gain (loss) on marketable securities	5,070						5,070	5,070
Reversal of unrealized gain to recognized gain on marketable securities	(16,373)						(16,373)	(16,373)
Distributions declared ($0.50 and $0.30 per weighted average number of common shares outstanding for the nine months ended September 30, 2012 and 2011, respectively)	(108,569)					(108,569)		(108,569)
Issuance of common stock, net of offering costs	266,491		37		266,454			266,491
Issuance of common stock, net of offering costs (in shares)			36,570
Redemption of fractional shares of common stock	(1,253)				(1,253)			(1,253)
Redemption of fractional shares of common stock (in shares)			(39)	(118)
Distribution reinvestment program (DRP)	11,626				11,626			11,626
Distribution reinvestment program (DRP) (in shares)			167	502
Issuance of restricted common stock (in shares)			8	24
Stock based compensation expense	220				220			220
Balance at Sep. 30, 2012	$ 2,278,575		$ 85	$ 146	$ 4,705,024	$ (2,436,010)	$ 7,836	$ 2,277,081	$ 1,494
Balance (in shares) at Sep. 30, 2012		85,088	85,088	145,555