RELATED PARTY TRANSACTIONS - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Related Party Transaction [Line Items]
Ratio of percentage of stockholders' equity			0.000875
Compensation and management fee	$ 45,983,000	$ 41,993,000	$ 136,091,000	$ 120,193,000
Management Agreement
Related Party Transaction [Line Items]
Compensation and management fee	46,000,000	42,000,000	136,100,000	120,200,000
Management fee payable	17,700,000		17,700,000		$ 13,800,000
Reimbursement payments	$ 3,700,000	$ 0	$ 3,100,000	$ 0
Renewal term			2 years
Accelerated period for agreement termination, if election to terminate is not made			90 days
Management Agreement | Minimum
Related Party Transaction [Line Items]
Accelerated period for agreement termination, if election to terminate is made			7 days
Management Agreement | Maximum
Related Party Transaction [Line Items]
Accelerated period for agreement termination, if election to terminate is made			90 days