CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (20,724)	$ (18,045)	$ (61,662)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	2,203	1,660	7,677
Asset write-downs and impairment of field equipment	49	75	241
Share-based compensation to employees	8,520	4,561	27,116
Increase in trade receivables	(1,672)	(5,486)	(23,228)
Amortization of discount	2,427	106	252
Decrease (increase) in receivables and prepaid expenses	(1,834)	(4,815)	1,979
Decrease (increase) in inventories	1,638	(400)	3,524
Increase in other long-term assets	(620)	(256)	(554)
Increase (decrease) in trade payables	2,213	(3,557)	(1,150)
Increase (decrease) in other payables and accrued expenses	(8,300)	(1,410)	14,460
Increase in employee benefit liabilities, net	76	109	440
Increase (decrease) in other long-term liabilities	(800)	550	(2,229)
Net cash used in operating activities	(16,824)	(26,908)	(33,134)
Cash flows from investing activities:
Purchase of property and equipment	(737)	(1,031)	(2,459)
Purchase of field equipment	(1,370)	(1,402)	(4,907)
Proceeds from maturity of short-term investments	45,000	60,000	120,000
Purchase of short-term investments	(44,750)	(44,654)	(104,006)
Net cash provided by (used in) investing activities	(1,857)	12,913	8,628
Cash flows from financing activities:
Proceeds from issuance of shares, net			1,540
Proceeds from long-term loan, net	149,150
Proceeds from other long-term loans			19
Repayment of long-term loan	(100,000)
Repayment of other long-term loan	(17)	(18)	(76)
Exercise of options and warrants	2,581	77	3,685
Net cash provided by financing activities	51,714	59	5,168
Effect of exchange rate changes on cash and cash equivalents	10	11	8
Increase (decrease) in cash, cash equivalents and restricted cash	33,043	(13,925)	(19,330)
Cash, cash equivalents and restricted cash at beginning of period	80,718	100,048	100,048
Cash, cash equivalents and restricted cash at the end of the period	113,761	86,123	80,718
Cash paid during the period for:
Income taxes	3,758	3,402	10,286
Interest	$ 3,009	$ 2,508	$ 10,162