OTHER INCOME (EXPENSE), NET - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Interest income	$ 8,100	$ 2,900	$ 20,200	$ 7,100
Net foreign currency exchange gains (losses)	800	(10,200)	2,900	(16,300)
Realized gains (losses) on investments	700	4,500	27,900	25,800
Mark-to-market charge on equity investments	800	1,500	1,300	12,200
Net unrealized gains on equity investments	$ (115)		$ 126,444
Other-than-temporary impairment charge		2,900		7,700
Other Nonoperating Income (Expense)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expense related to repricing of debt		$ 2,100		2,100
The Princeton Review | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Other Nonoperating Income (Expense)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of business				$ (1,200)