INCOME TAXES - Additional Tax Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Income tax expense recognized	$ 60,400
Accrued interest and penalties	0	$ 0
Uncertain Tax Positions
Unrecognized tax benefits	15,185	15,342	$ 15,413	$ 15,488
Gross decrease in tax portions from prior years		$ (71)	$ (75)
Gross decrease in tax portions from current year	(157)
Unrecognized tax benefits would affect the effective income tax rate if recognized	8,000
Federal
Income Taxes
Net operating loss carryforwards	400,000
Net operating loss carryforwards, indefinite period	2,000
Tax credit carryforward amount	43,600
State
Income Taxes
Net operating loss carryforwards	650,700
State | Research and development
Income Taxes
Tax credit carryforward amount	$ 32,200