SUPPLEMENTAL CASH FLOW INFORMATION - Supplemental Cash Flow Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Supplemental Cash Flow Data:
Cash paid for interest	$ 397	$ 538
Cash paid for income taxes	2,599	1,342
Supplemental disclosures of non-cash investing and financing activities:
Right-of-use assets obtained in exchange for operating lease obligations	255,553	19,918
Change in purchases of property and equipment in accounts payable and accrued expenses	10,354	13,114
Unpaid business combination purchase price	7,338	6,447
Fair value of common stock issued related to business combination	(14,999)	0
Recovery of common stock in connection with indemnification settlement agreement	0	789
Fair value of common stock issued to settle the conversion of senior notes, due 2022	$ (77,614)	$ 0