Related Party Arrangements - Adviser and Former Adviser Earned Fees and Incurred Reimbursable Expenses (Detail) - USD ($)		12 Months Ended
	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Acquisition fees:
Acquisition fees from offering proceeds		$ 0	$ 0	$ 319,000
Acquisition fees from debt proceeds		0	0	1,521,000
Total		0	0	1,840,000
Asset management fees		12,137,000	19,726,000	29,863,000
Reimbursable expenses:
Acquisition costs		0	0	248,000
Operating expenses		5,267,000	5,451,000	6,680,000
Total		5,267,000	5,451,000	6,928,000
Total fees earned and reimbursable expenses		17,404,000	25,177,000	38,631,000
Acquisition fee as a percentage of offering proceeds	3.00%
Acquisition fee as a percentage of loan proceeds	3.00%
Asset management fees to advisor		11,914,000	15,666,000	18,651,000
Advisor
Reimbursable expenses:
Acquisition costs		0	0	40,000
Operating expenses		$ 300,000	400,000	400,000
As percentage of average invested assets
Reimbursable expenses:
Maximum reimbursement of expenses, percent		2.00%
As percentage of net income
Reimbursable expenses:
Maximum reimbursement of expenses, percent		25.00%
Assets Held-for-sale
Reimbursable expenses:
Asset management fees to advisor		$ 200,000	$ 4,100,000	$ 11,200,000