SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Changes in operating assets and liabilities
Accounts receivable, net	$ 10,395	$ 19,425
Inventories	(880)	1,085
Other current assets and other assets	(1,433)	650
Income taxes	(355)	12,255
Accounts payable	(6,511)	552
Accrued expenses and other current liabilities	492	(5,067)
Accrued compensation related costs	(32,970)	(35,789)
Other liabilities	(1,829)	(2,537)
Operating lease liabilities	(10,082)
Changes in operating assets and liabilities on cash flows from operating activities	(43,173)	(9,426)
Non-cash financing and investing activities:
Issuance of seller notes in connection with acquisitions	4,451
Additions to property, plant and equipment acquired through financing obligations		1,208
Retirements of financed property, plant and equipment and related obligations		2,246
Purchase of property, plant and equipment in accounts payable at period end	$ 4,443	$ 545