Selected Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 94,543	$ 95,511	$ 94,041	$ 92,960	$ 88,112		$ 79,904		$ 67,476		$ 65,033		$ 377,055	$ 300,525		$ 181,084
Operating income (loss)	5,764	3,660	2,714	(991)	(4,824)		(7,925)		(3,650)		(7,909)		11,147	(24,308)		(23,178)
Net income (loss) attributable to common stockholders	$ 6,839	$ (11,992)	$ (12,072)	$ (14,442)	$ (17,420)		$ (19,225)		$ (13,410)		$ (18,000)		$ (31,667)	$ (68,055)		$ (52,511)
Weighted average number of shares outstanding(basic and diluted)	175,328	175,033	175,489	174,681	173,766	[1]	162,730	[1]	146,257	[1]	131,880	[1]	175,121	153,804	[1]	85,710
Income (loss) per share of common stock(basic and diluted)	$ 0.04	$ (0.07)	$ (0.07)	$ (0.08)	$ (0.10)		$ (0.12)		$ (0.09)		$ (0.14)		$ (0.18)	$ (0.44)		$ (0.61)

[1] For the purposes of determining the weighted average number of shares of common stock outstanding, stock distributions issued are treated as if they were outstanding for all periods presented.