INCOME TAXES - Provision for Income Taxes Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income tax expense reconciliation (percent)
Expected federal income tax	21.00%	21.00%	21.00%
State income taxes	8.70%	(26.10%)	8.00%
Permanent items	14.90%	(6.50%)	1.10%
Research and development tax credits	(7.20%)	(17.10%)	1.60%
Excess tax benefits and stock-based compensation	(12.70%)	(13.90%)	(1.00%)
Acquisition-related tax adjustments	0.00%	3.20%	(2.10%)
Enactment of the CARES Act	(72.20%)	0.00%	0.00%
Other	1.50%	7.10%	(1.70%)
Income tax benefit	(46.00%)	(32.30%)	26.90%
Income tax expense reconciliation
Expected federal income tax	$ 3,247	$ 1,234	$ (11,247)
State income taxes	1,347	(1,536)	(4,270)
Permanent items	2,303	(384)	(614)
Research and development tax credits	(1,119)	(1,003)	(850)
Excess tax benefits and stock-based compensation	(1,960)	(815)	559
Acquisition-related tax adjustments	0	189	1,144
Enactment of the CARES Act	11,164	0	0
Other	228	418	885
Total benefit from income taxes	$ (7,118)	$ (1,897)	$ (14,393)