SHAREHOLDERS' EQUITY - Summary of Changes in Shares Outstanding and Aggregate Par Value of Outstanding Shares for Each Class of Common Stock (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemptions of common stock, shares	(1,155)	(2,862)	(1,906)
Class A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, shares	105,674	104,589	99,374
Issuance of common stock, Primary shares, shares			3,696
Issuance of common stock, DRIP shares, shares	1,719	2,601	2,910
Issuance of common stock, Stock grants, shares	158	180	151
Redemptions of common stock, shares	(1,588)	(1,678)	(1,537)
Forfeitures of common stock, shares	(6)	(18)	(5)
Ending balance, shares	105,957	105,674	104,589
Class T
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, shares	71,280	69,925	58,032
Issuance of common stock, Primary shares, shares			10,468
Issuance of common stock, DRIP shares, shares	1,133	1,736	1,794
Issuance of common stock, Stock grants, shares	0	0	0
Redemptions of common stock, shares	(370)	(381)	(369)
Forfeitures of common stock, shares	0	0	0
Ending balance, shares	72,043	71,280	69,925
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, shares	176,954	174,514	157,406
Issuance of common stock, Primary shares, shares			14,164
Issuance of common stock, DRIP shares, shares	2,852	4,337	4,704
Issuance of common stock, Stock grants, shares	158	180	151
Redemptions of common stock, shares	(1,958)	(2,059)	(1,906)
Forfeitures of common stock, shares	(6)	(18)	(5)
Ending balance, shares	178,000	176,954	174,514