SUPPLEMENTAL CASH FLOW INFORMATION - Supplemental Disclosures of Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Data:
Cash paid for interest	$ 5,677	$ 4,125	$ 1,374
Cash paid for income taxes	2,744	1,622	1,254
Supplemental disclosures of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for operating lease obligations	40,555
Change in purchases of property and equipment in accounts payable and accrued expenses	(419)	15,067	143
Unpaid business combination purchase price	8,411	3,995	2,115
Non-cash proceeds from sale of asset group	100,000	0	0
Fair value of common stock issued related to business combination	0	(140,107)	0
Recovery of common stock in connection with indemnification settlement agreement	789	2,745	0
Fair value of common stock issued to settle the conversion of senior notes, due 2022	0	(571,408)	0
Fair value of shares received to settle senior note hedges, due 2022	$ 0	$ 544,276	$ 0