SHAREHOLDERS' EQUITY - Narrative (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 02, 2017 USD ($)	Dec. 31, 2018 USD ($) warrant exchangeable_note vote $ / shares shares	Dec. 31, 2017 USD ($) warrant exchangeable_note $ / shares shares	Dec. 31, 2016 USD ($) shares	May 03, 2016 shares
Class of Stock
Directors elected (as a percent)		25.00%
Proceeds from issuance of warrants | $	$ 23,600	$ 0	$ 23,650	$ 0
Warrants exercised during period | warrant		0	0
Exchangeable notes exchanged during period | exchangeable_note		0	0
Trade date fair value of shares acquired during period | $		$ 82,891	$ 50,121	$ 315,250
Class B Convertible Common Stock
Class of Stock
Number of votes | vote		10
Common Stock
Class of Stock
Number of votes | vote		1
Common stock reserved (shares)		28,000,000
Treasury stock acquired during period (shares)		500,000	700,000	6,300,000
Trade date fair value of shares acquired during period | $		$ 82,900	$ 50,100	$ 315,300
Number of shares authorized to be repurchased (shares)					10,000,000
Remaining number of shares authorized to be repurchased (shares)		8,000,000
Senior Notes | IAC
Class of Stock
Class of warrant outstanding (shares)		3,400,000	3,400,000
Exercise price of warrants (USD per share) | $ / shares		$ 229.70	$ 229.70
Proceeds from issuance of warrants | $	$ 23,600