Dividends/Distributions - Additional Information (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
Dividends [Line Items]
Distributions paid, per share	$ 0.75	$ 0.69	$ 1.50	$ 1.37
Distributions paid, preferred stockholders	$ 91	$ 91	$ 182	$ 182
Distributions paid, preferred stockholders, per share	$ 15.95	$ 15.95	$ 31.90	$ 31.90
Taxable Income Distribution [Member]
Dividends [Line Items]
Distributions paid	$ 72,912	$ 66,590	$ 145,646	$ 131,813
Distributions paid, per share	$ 0.75	$ 0.69	$ 1.50	$ 1.37