Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended								12 Months Ended
	Jun. 30, 2015	May. 31, 2015	Apr. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Apr. 30, 2014	Jan. 31, 2014	May. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Net proceeds									$ 1,029,540	$ 766,138	$ 633,807
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued	11,500,000	280,025	23,000,000	100,000	9,200,000	9,200,000	9,775,000	25,875,000	34,780,025	28,275,000
Share issue price	$ 29.42	$ 29.97	$ 29.75	$ 27.58	$ 27.49	$ 27.72	$ 26.25		$ 29.64	$ 27.14
Net proceeds	$ 337,918	$ 7,895	$ 683,722	$ 2,758	$ 252,530	$ 254,758	$ 256,092		$ 1,029,535	$ 766,138