CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss		$ (65,323)	$ (39,265)	$ (663,925)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization		62,041	60,535	83,069
Stock-based compensation		27,260	31,295	34,733
Lower of cost or market adjustment		12,883	11,053	21,550
Impairment of assets		2,427	8,618	544,611
Provision for bad debts		1,051	1,552	3,766
Provision for arbitration award				11,282
Provision for deferred income taxes		(5,567)	(6,566)	(2,875)
(Gain) loss on the disposition of property and equipment			1,465	(43)
Changes in operating accounts, net of acquisitions:
Accounts receivable		3,987	26,255	20,534
Inventories		(17,716)	(20,656)	(37,216)
Prepaid expenses and other current assets		(49,834)	(3,895)	16,900
Accounts payable		12,448	(4,975)	(20,049)
Accrued and other current liabilities		50,209	(7,670)	(10,320)
All other operating activities		(7,925)	(265)	(4,848)
Net cash provided by (used in) operating activities		25,941	57,481	(2,831)
Cash flows from investing activities:
Cash paid for acquisitions, net of cash assumed		(34,291)		(91,799)
Purchases of property and equipment		(30,881)	(16,567)	(22,399)
Additions to license and patent costs		(1,159)	(1,132)	(907)
Proceeds from disposition of property and equipment		273	350
Purchase of noncontrolling interest		(2,250)	(3,533)
Other investing activities		(2,351)	(1,000)	(5,750)
Net cash used in investing activities		(70,659)	(21,882)	(120,855)
Cash flows from financing activities:
Payments related to net-share settlement of stock-based compensation		(5,545)	(2,871)	(1,108)
Payments on earnout consideration		(3,206)
Repayment of capital lease obligations		(437)	(1,055)	(1,049)
Net cash used in financing activities		(9,188)	(3,926)	(2,157)
Effect of exchange rate changes on cash and cash equivalents		5,303	(2,369)	(3,376)
Net increase (decrease) increase in cash and cash equivalents		(48,603)	29,304	(129,219)
Cash and cash equivalents at the beginning of the period		184,947	155,643	284,862
Cash and cash equivalents at the end of the period		136,344	184,947	155,643
Supplemental Cash Flow Information:
Cash interest payments		503	839	707
Cash income tax payments, net		6,339	11,045	12,512
Transfer of equipment from inventory to property and equipment, net	[1]	9,881	12,493	9,902
Transfer of equipment to inventory from property and equipment, net	[2]	378	$ 1,102	$ 2,764
Stock issued for acquisitions of businesses		$ 3,208

[1] Inventory is transferred from inventory to property and equipment at cost when the Company requires additional machines for training or demonstration or for placement into on demand manufacturing services locations.

[2] In general, an asset is transferred from property and equipment, net into inventory at its net book value when the Company has identified a potential sale for a used machine.