INCOME TAXES - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 30, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2018
Income Taxes [Line Items]
Effective income tax rate (benefit) expense, percent		20.20%	18.50%	19.40%	17.90%
Income tax expense (benefit)		$ 11,654	$ 9,217	$ 33,368	$ 17,355
Long-term asset		133,111		$ 133,111		$ 103,341
Withholding and interest for licencing and royalty payments	$ 13,200
Withholding and interest for licencing and royalty payments period	3 years
State and foreign income tax returns subject to examination period minimum (in years)				3 years
State and foreign income tax returns subject to examination period maximum (in years)				4 years
Reduction of Korean Withholding Taxes [Member]
Income Taxes [Line Items]
Reduction of deferred tax asset for foreign tax credits and R&D				$ 20,700		20,700
U.S.Federal Government [Member]
Income Taxes [Line Items]
Estimated settlement amounts due (refunds) from withholding taxes							$ 16,200
Korean Government [Member]
Income Taxes [Line Items]
Estimated settlement amounts due (refunds) from withholding taxes							$ 36,900
Allocation of Withholding to Non-Korean Patents [Member]
Income Taxes [Line Items]
Long-term asset		49,900		49,900		40,100
Allocation of Withholding to Non-Korean Patents [Member] | U.S.Federal Government [Member]
Income Taxes [Line Items]
Estimated settlement amounts due (refunds) from withholding taxes		$ 42,500		$ 42,500		$ 32,700