Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Common Stock USD ($)	Additional Paid-In Capital USD ($)	Cumulative Dividends in Excess of Earnings USD ($)	Total Stockholders’ Equity USD ($)	Noncontrolling Interest USD ($)	Common Stock	Class A Common Stock	Class B Common Stock
Beginning balance at Dec. 31, 2009	$ 1,071,317	$ 1,405	$ 1,251,996	$ (182,084)	$ 1,071,317	$ 0
Beginning balance, shares at Dec. 31, 2009							140,591,000	0	0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock (in shares)							61,191,000	0	0
Issuance of common stock	594,677	615	594,062	0	594,677	0
Offering costs	(56,621)	0	(56,621)	0	(56,621)	0
Issuance of restricted common stock (in shares)							357,000	0	0
Issuance of restricted common stock	0	0	0	0	0	0
Share-based compensation expense	1,313	0	1,313	0	1,313	0
Issuance of common stock under the DRIP (in shares)							5,953,000	0	0
Issuance of common stock under the DRIP	56,551	60	56,491	0	56,551	0
Repurchase and cancellation of common stock (in shares)							(5,448,000)	0	0
Repurchase and cancellation of common stock	(51,856)	(54)	(51,802)	0	(51,856)	0
Distributions ($0.64 per common share)	(120,507)	0	0	(120,507)	(120,507)	0
Adjustment to redeemable noncontrolling interests	275	0	(26)	301	275	0
Net Income (loss) attributable to controlling interest	(7,903)	0	0	(7,903)	(7,903)	0
Ending balance at Dec. 31, 2010	1,487,246	2,026	1,795,413	(310,193)	1,487,246	0
Ending balance, shares at Dec. 31, 2010							202,644,000	0	0
Increase (Decrease) in Stockholders' Equity
Issuance of common stock (in shares)							21,682,000	0	0
Issuance of common stock	214,641	216	214,425	0	214,641	0
Offering costs	(18,896)	0	(18,896)	0	(18,896)	0
Issuance of restricted common stock (in shares)							62,000	0	0
Issuance of restricted common stock	0	1	(1)	0	0	0
Share-based compensation expense	3,221	0	3,221	0	3,221	0
Issuance of common stock under the DRIP (in shares)							7,986,000	0	0
Issuance of common stock under the DRIP	75,864	80	75,784	0	75,864	0
Repurchase and cancellation of common stock (in shares)							(3,883,000)	0	0
Repurchase and cancellation of common stock	(37,680)	(39)	(37,641)	0	(37,680)	0
Distributions ($0.64 per common share)	(162,597)	0	0	(162,597)	(162,597)	0
Net Income (loss) attributable to controlling interest	5,541	0	0	5,541	5,541	0
Ending balance at Dec. 31, 2011	1,567,340	2,284	2,032,305	(467,249)	1,567,340	0
Ending balance, shares at Dec. 31, 2011							228,491,000	0	0
Increase (Decrease) in Stockholders' Equity
Issuance of restricted common stock (in shares)							626,000	333,000	12,000
Issuance of restricted common stock	0	10	(10)	0	0	0
Share-based compensation expense	17,408	0	6,964	0	6,964	10,444
Issuance of common stock under the DRIP (in shares)							3,362,000	0	0
Issuance of common stock under the DRIP	31,916	34	31,882	0	31,916	0
Tender repurchase and cancellation of common stock (in shares)							0	(14,851,000)	0
Tender repurchase and cancellation of common stock	(152,879)	(149)	(152,730)	0	(152,879)	0
Repurchase and cancellation of common stock (in shares)							(3,070,000)	(107,000)	(144,000)
Repurchase and cancellation of common stock	(32,607)	(32)	(32,575)	0	(32,607)	0
Conversion (in shares)							(229,409,000)	114,711,000	114,698,000
Distributions ($0.64 per common share)	(142,159)	0	0	(142,044)	(142,044)	(115)
Net Income (loss) attributable to controlling interest	(24,424)	0	0	(24,424)	(24,424)	0
Ending balance at Dec. 31, 2012	$ 1,264,595	$ 2,147	$ 1,885,836	$ (633,717)	$ 1,254,266	$ 10,329
Ending balance, shares at Dec. 31, 2012							0	100,086,000	114,566,000