Equity and Redeemable Non-controlling Interest - Schedule of Company's Outstanding Shares of Common Stock (Detail)	9 Months Ended
	Sep. 30, 2018 shares
Class of Stock [Line Items]
Beginning balance	170,384,000
Common stock issued	193,936,000
Distribution reinvestment	6,247,000
Common stock repurchased	(2,853,000)
Independent directors' restricted stock grant	37,000
Ending balance	367,751,000
Class S Shares [Member]
Class of Stock [Line Items]
Beginning balance	130,085,145
Common stock issued	104,482,000
Distribution reinvestment	4,217,000
Common stock repurchased	(1,521,000)
Ending balance	237,262,632
Class T Shares [Member]
Class of Stock [Line Items]
Beginning balance	5,624,614
Common stock issued	13,387,000
Distribution reinvestment	238,000
Common stock repurchased	(23,000)
Ending balance	19,227,318
Class D Shares [Member]
Class of Stock [Line Items]
Beginning balance	3,955,114
Common stock issued	20,084,000
Distribution reinvestment	255,000
Common stock repurchased	(115,000)
Ending balance	24,178,629
Class I Shares [Member]
Class of Stock [Line Items]
Beginning balance	30,719,160
Common stock issued	55,983,000
Distribution reinvestment	1,537,000
Common stock repurchased	(1,194,000)
Independent directors' restricted stock grant	37,000
Ending balance	87,082,488