SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recent Accounting Pronouncements (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) lease	Dec. 31, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity investment portfolio balance	$ 3,000
Right of use leased asset	5,572		$ 5,572
Reclassification of stranded tax effects in AOCI	0
Adjustments for New Accounting Principle, Early Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of stranded tax effects in AOCI	$ 1,800
Scenario, Forecast | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Right of use leased asset		$ 10,000
Number of leased facilities | lease		15