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	Jun. 30, 2018	Dec. 31, 2017
Assets:
Equity securities	$ 320	$ 270
Investments measured at net asset value - trading securities	24,705	23,463
Quoted prices in active markets for identical assets (Level 1)
Assets:
Equity securities	320	270
Significant other observable inputs (Level 2)
Assets:
Equity securities	0	0
Significant unobservable inputs (Level 3)
Assets:
Equity securities	$ 0	$ 0