CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Cash flows from operating activities:
Net loss	$ (5,128)	$ (23,305)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	2,276	2,328
Provision for doubtful accounts	600	142
Asset impairment and restructuring	0	1,920
Amortization of debt issuance costs	537	945
Stock-based compensation	1,571	1,929
Changes in operating assets and liabilities:
Accounts receivable	9,125	11,975
Inventory	7,457	(1,848)
Prepaid expenses and other assets	(1,039)	(3,114)
Accounts payable, accrued and other liabilities	(11,667)	(17,458)
Warranty obligations	809	580
Deferred revenues	(1,180)	1,395
Net cash provided by (used in) operating activities	3,361	(24,511)
Cash flows from investing activities:
Purchases of property and equipment	(1,043)	(3,466)
Net cash used in investing activities	(1,043)	(3,466)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	19,923	26,522
Proceeds from debt	2,309	24,162
Principal payments on term debt	(771)	0
Payments under revolving credit facility	0	(10,100)
Proceeds from issuance of common stock under employee stock plans	269	2
Net cash provided by financing activities	21,730	40,586
Effect of exchange rate changes on cash	63	(418)
Net increase in cash and cash equivalents	24,111	12,191
Cash and cash equivalents—Beginning of period	29,144	17,764
Cash and cash equivalents—End of period	53,255	29,955
Supplemental disclosures of non-cash investing and financing activities:
Purchases of fixed and intangible assets included in accounts payable	117	1,309
Deferred debt and offering costs included in accounts payable	0	231
Warrants issued in connection with debt	$ 0	$ 1,447