CONTRACT LIABILITIES (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2020 CNY (¥)	Dec. 31, 2020 USD ($)	[1]	Dec. 31, 2019 CNY (¥)
CONTRACT LIABILITIES [abstract]
Contract liabilities - advances received from customers	¥ 186,959			¥ 438,705
Contract liabilities - frequent traveler program	28,346			20,115
Contract liabilities	¥ 215,305	$ 32,996		¥ 458,820

[1] Translation of amounts from Renminbi ("RMB") into United States dollars ("US$") for the convenience of the reader has been made at US$1.00=RMB6.5250, the certified exchange rates for December 31, 2020 as published by the Federal Reserve Board of the United States. No representation is made that the RMB amounts could have been, or could be, converted into US$ at that rate on December 31, 2020 or on any other date.