FAIR VALUE DISCLOSURES - Valuation of financial instruments measured at fair value on a recurring basis (Details) - Fair value on a recurring basis - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Equity securities	$ 248	$ 211
Investments measured at net asset value	25,668	22,815
Quoted prices in active markets for identical assets (Level 1)
Assets:
Equity securities	248	211
Significant other observable inputs (Level 2)
Assets:
Equity securities	0	0
Significant unobservable inputs (Level 3)
Assets:
Equity securities	$ 0	$ 0