Segment Reporting - Summary of Total Assets by Segment (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total assets	$ 11,727,174	$ 4,625,308
Multifamily [Member]
Segment Reporting Information [Line Items]
Total assets	5,379,132	2,567,735
Industrial [Member]
Segment Reporting Information [Line Items]
Total assets	2,876,939	636,900
Hotel [Member]
Segment Reporting Information [Line Items]
Total assets	1,125,262	281,242
Retail [Member]
Segment Reporting Information [Line Items]
Total assets	138,091	103,138
Real Estate-Related Securities [Member]
Segment Reporting Information [Line Items]
Total assets	2,040,501	918,975
Other (Corporate) [Member]
Segment Reporting Information [Line Items]
Total assets	$ 167,249	$ 117,318