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	Sep. 30, 2017	Dec. 31, 2016
Assets:
Available-for-sale securities - equity securities	$ 289	$ 264
Investments measured at net asset value - trading securities	21,788	18,367
Quoted prices in active markets for identical assets (Level 1)
Assets:
Available-for-sale securities - equity securities	289	264
Significant other observable inputs (Level 2)
Assets:
Available-for-sale securities - equity securities	0	0
Significant unobservable inputs (Level 3)
Assets:
Available-for-sale securities - equity securities	$ 0	$ 0