Summary of Dividend Distribution Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Distributions declared to common stockholders	$ 305,691	$ 277,456
Distributions declared per common share	$ 0.30	$ 0.30
Distributions paid to common stockholders after period end	$ 305,691	$ 277,456
Distributions paid per common share after period end	$ 0.30	$ 0.30
Date of distributions paid to common stockholders after period end	Apr. 28, 2017	Apr. 29, 2016
7.875% Series A Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 3,648	$ 3,648
Preferred series dividends declared, per share	$ 0.492	$ 0.492
7.625% Series C Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 5,719	$ 5,719
Preferred series dividends declared, per share	$ 0.477	$ 0.477
7.50% Series D Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 8,625	$ 8,625
Preferred series dividends declared, per share	$ 0.469	$ 0.469
7.625% Series E Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Preferred dividends declared	$ 5,481
Preferred series dividends declared, per share	$ 0.477