BASIS OF PRESENTATION - Adoption of 2020-06 (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax liabilities	$ 70,325	$ 16,190
Long-term convertible securities	563,697	474,834
Retained earnings	$ 653,184	532,265
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred tax liabilities		(20,600)
Retained earnings		(2,800)
Additional paid-in capital		(63,300)
Cumulative Effect, Period of Adoption, Adjustment, Debt Discount Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term convertible securities		89,100
Cumulative Effect, Period of Adoption, Adjustment, Debt Discount Amortization and Equity Costs Reclassification
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term convertible securities		$ (2,500)