FAIR VALUE MEASUREMENTS Equity investments without readily determinable fair values and derivatives (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Sep. 12, 2016	Dec. 11, 2015	May 26, 2015	Aug. 07, 2014
Fair Value Disclosures [Abstract]
Cost Method Investments			$ 450,900
Equity Investments without Readily Determinable Fair Value	$ 450,900
Derivatives Not Designated as Hedging Instruments
Foreign currency gains (losses), net of derivative activity	(5,400)	$ (5,900)
Foreign Currency Contracts, Translation Risk
Derivatives Not Designated as Hedging Instruments
Foreign currency derivative instruments not designated as hedging instruments at fair value, net	0		0
Foreign Currency Contracts, Transaction Risk
Derivatives Not Designated as Hedging Instruments
Foreign currency gains (losses) recorded in Foreign currency transactions and other	20,600	6,800
Foreign Currency Contracts
Derivatives Not Designated as Hedging Instruments
Net cash inflow from settlement of derivative contracts included in operating activities	18,200	$ 2,700
Ctrip.com International, Ltd. | Ctrip convertible debt securities | Long-term Investments
Derivatives Not Designated as Hedging Instruments
Cost of Ctrip convertible notes	1,275,000			$ 25,000	$ 500,000	$ 250,000	$ 500,000
Embedded derivative, fair value of embedded derivative	$ 2,100		$ 1,800