SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounting Guidance Not Yet Effective (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) lease	Jan. 01, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground leases | lease	8
Office building leases | lease	1
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Weighted-average remaining term of leases	43 years 8 months 12 days
Weighted-average discount rate of leases (as a percent)	8.00%
Deferred lease costs and capitalized overhead recorded	$ 3,887
Legal and other costs related to future leases	$ 938
Forecast | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right-of-use assets		$ 4,358
Lease liabilities		$ 4,358