CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net loss		$ (45,263)	$ (65,323)	$ (39,265)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization		59,293	62,041	60,535
Stock-based compensation		29,253	27,260	31,295
Lower of cost or market adjustment		0	12,883	11,053
Impairment of assets		1,998	2,427	8,618
Provision for bad debts		1,824	1,051	1,552
Provision for deferred income taxes		(2,990)	(5,567)	(6,566)
Loss on the disposition of property and equipment		0	0	1,465
Changes in operating accounts, net of acquisitions:
Accounts receivable		599	3,987	26,255
Inventories		(34,035)	(17,716)	(20,656)
Prepaid expenses and other current assets		40,922	(49,834)	(3,895)
Accounts payable		11,559	12,448	(4,975)
Accrued and other current liabilities		(50,234)	50,209	(7,670)
All other operating activities		(8,130)	(7,739)	(263)
Net cash provided by operating activities		4,796	26,127	57,483
Cash flows from investing activities:
Cash paid for acquisitions, net of cash assumed		0	(34,291)	0
Purchases of property and equipment		(40,694)	(30,881)	(16,567)
Additions to license and patent costs		(970)	(1,159)	(1,132)
Proceeds from disposition of property and equipment		333	273	350
Purchase of noncontrolling interest		0	(2,250)	(3,533)
Other investing activities		(496)	(2,351)	(1,000)
Net cash used in investing activities		(41,827)	(70,659)	(21,882)
Cash flows from financing activities:
Proceeds from borrowings		25,000	0	0
Payments related to net-share settlement of stock-based compensation		(7,367)	(5,545)	(2,871)
Payments on earnout consideration		(2,675)	(3,206)	0
Repayment of capital lease obligations		(694)	(437)	(1,055)
Net cash provided by (used in) financing activities		14,264	(9,188)	(3,926)
Effect of exchange rate changes on cash and cash equivalents		(3,145)	5,303	(2,369)
Net (decrease) increase in cash and cash equivalents		(25,912)	(48,417)	29,306
Cash, cash equivalents and restricted cash at the beginning of the period	[1]	136,831	185,248	155,942
Cash, cash equivalents and restricted cash at the end of the period	[1]	110,919	136,831	185,248
Supplemental Cash Flow Information [Abstract]
Cash interest payments		542	503	839
Cash income tax payments, net		8,964	6,339	11,045
Transfer of equipment from inventory to property and equipment, net	[2]	5,612	9,881	12,493
Transfer of equipment to inventory from property and equipment, net	[3]	2,563	378	1,102
Stock issued for acquisitions of businesses		0	3,208	0
Restricted cash		$ 921	$ 487	$ 301

[1] The amounts for cash and cash equivalents shown above include restricted cash of $921, $487, $301 and $299 as of December 31, 2018, 2017, 2016 and 2015, respectively, which were included in other assets, net, in the Consolidated Balance Sheets.

[2] 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.

[3] In general, an asset is transferred from property and equ