Common Stock and Other Equity Related Transactions - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	6 Months Ended		3 Months Ended						3 Months Ended
	Mar. 04, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Common Stock	Mar. 31, 2011 Common Stock	Jun. 30, 2011 Series A Preferred Stock	Mar. 31, 2011 Series A Preferred Stock	Mar. 31, 2011 $150 million Series D 8% Units	Jun. 30, 2011 $150 million Series D 8% Units	Mar. 31, 2011 $50 million of Series F 7.95% Units	Jun. 30, 2011 $50 million of Series F 7.95% Units
Class of Stock [Line Items]
Common stock issued in equity offering		6,000,000
Net proceeds from issuance of Common Stock		$ 344,049
8.034% Series A Cumulative Redeemable Perpetual Preferred Stock, shares issued	8,000,000	8,000,000	0
8.034% Series A Cumulative Redeemable Perpetual Preferred Stock, par value per share	$ 0.01	$ 0.01	$ 0.01
8.034% Series A Cumulative Redeemable Perpetual Preferred Stock, liquidation preference	$ 25.00
8.034% Series A Cumulative Redeemable Perpetual Preferred Stock, conversion Price per share	$ 24.75
Conversion of OP Units to redeemable preferred stock	$ 200,000		$ 200,000						$ 150,000		$ 50,000
8.034% Series A Cumulative Redeemable Perpetual Preferred Stock, redemption price	$ 25.00
Dividend distribution to common stock holders				$ 0.375	$ 0.375
Dividend record date				Jun. 24, 2011	Mar. 25, 2011	Jun. 10, 2011	Mar. 21, 2011
Dividend payment date				Jul. 08, 2011	Apr. 08, 2011	Jun. 30, 2011	Mar. 31, 2011
Dividend distribution to Preferred Stock holders						$ 0.502125	$ 0.156217
Preferred stock, dividend rate	8.034%							8.0625%		7.95%