Summary of Dividend Distribution Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Class of Stock [Line Items]
Distributions declared to common stockholders			$ 554,935	$ 568,641
Distributions declared per common share	$ 0.30	$ 0.30	$ 0.60	$ 0.60
Distributions paid to common stockholders after period end			$ 277,479	$ 284,331
Distributions paid per common share after period end			$ 0.30	$ 0.30
Date of distributions paid to common stockholders after period end			Jul. 29, 2016	Jul. 30, 2015
7.875% Series A Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared			$ 7,296	$ 7,296
Preferred series dividends declared, per share			$ 0.984	$ 0.984
7.625% Series C Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared			$ 11,438	$ 11,438
Preferred series dividends declared, per share			$ 0.953	$ 0.953
7.50% Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared			$ 17,250	$ 17,250
Preferred series dividends declared, per share			$ 0.938	$ 0.938