Related Party Arrangement, Fees and Expenses Incurred (Detail) - USD ($) $ / shares in Units, shares in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Asset management fees		$ 25,443,000	$ 17,892,000	$ 8,481,000
Cash distributions on Restricted Stock		31,454,000	$ 26,373,000	$ 14,203,000
Stock distributions, shares			3,200	2,400
Expense Support Agreements
Related Party Transaction [Line Items]
Asset management fees	[1]	$ 2,918,000	$ 4,379,000	$ 4,867,000
Then-current offering price or NAV	[2]	$ 10.04	$ 10.19	$ 10.24
Restricted Stock shares	[3]	291	423	478
Asset management fees	[1]	$ 13,565
Then-current offering price or NAV	[2]	$ 9.75
Expense Support Agreements | Restricted Stock
Related Party Transaction [Line Items]
Cash distributions on Restricted Stock	[4]	$ 427,000	$ 281,000	$ 98,000
Stock distributions, shares	[5]		14	7
Restricted Stock shares	[3]	1,332
Cash distributions on Restricted Stock	[4]	$ 810,000
Stock distributions on Restricted Stock	[5]	21

[1] No other amounts have been settled in connection with the Expense Support Agreements for the years ended December 31, 2016, 2015 and 2014, and cumulatively as of December 31, 2016.

[2] The number of restricted stock shares granted to the Advisor in lieu of payment in cash is determined by dividing the expense support amount for the respective determination date by the then-current public offering price as of the Original Determination Date or by the then-current NAV per share as of the Amended Determination Date.

[3] Restricted stock shares are comprised of approximately 1.0 million issued to the Advisor and approximately 0.3 million issuable to the Advisor as of December 31, 2016. No fair value was assigned to the restricted stock shares as the shares were valued at zero, which represents the lowest possible value estimated at vesting. In addition, the restricted stock shares were treated as unissued for financial reporting purposes because the vesting criteria had not been met as of December 31, 2016.

[4] The cash distributions have been recognized as compensation expense as issued and included in general and administrative expense in the accompanying consolidated statements of operations.

[5] This represents the number of shares issued to the Advisor as stock distributions on its restricted stock shares. The par value of the stock distributions has been recognized as compensation expense as issued and included in general and administrative expense in the accompanying consolidated statements of operations.