INCOME TAXES - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Reserves and accruals	$ 24,833	$ 21,823
Net operating loss carryforwards	33,070	39,733
Research and development credit carryforwards	39,730	38,179
Deferred stock-based compensation	1,354	1,202
Intangibles	7,321	7,838
Operating lease liabilities	8,697	7,822
Capitalized research and development expenses	9,681	10,805
Other	31	442
Gross deferred tax assets	124,717	127,844
Valuation allowance	(90,247)	(99,585)	$ (95,518)	$ (77,144)
Gross deferred tax assets after valuation allowance	34,470	28,259
Deferred tax liabilities:
Depreciation	(6,597)	(6,399)
Convertible notes	(3,652)	(4,708)
Operating lease right-of-use assets	(7,402)	(6,529)
Other	0	0
Gross deferred tax liabilities	(17,651)	(17,636)
Net deferred tax assets	$ 16,819	$ 10,623