Related Party Transactions - Summary of Components of Due to Affiliates (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Total components due to affiliates	$ 301,581	$ 133,071
Accrued Stockholder Servicing Fee [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	238,496	102,076
Performance Participation Allocation [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	37,484	16,974
Advanced Organization and Offering Costs [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	8,181	10,160
Accrued Management Fee [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	5,124	1,904
Accrued Affiliate Incentive Compensation Awards [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	4,714
Accrued Affiliate Service Provider Expenses [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	3,115	1,485
Other [Member]
Related Party Transaction [Line Items]
Total components due to affiliates	$ 4,467	$ 472