CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ (12,150)	$ (20,724)	$ (63,559)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	1,929	2,203	9,006
Asset write-downs and impairment of field equipment	75	49	407
Share-based compensation to employees	9,649	8,520	39,846
Decrease (increase) in trade receivables	(2,697)	(1,672)	(4,151)
Amortization of discount (premium)	(578)	2,427	1,022
Decrease (increase) in receivables and prepaid expenses	661	(1,834)	(6,174)
Decrease (increase) in inventories	(1,583)	1,638	(529)
Decrease (increase) in other long-term assets	(1,899)	(620)	(949)
Decrease (increase) in right of use assets, net	1,813
Increase (decrease) in trade payables	3,235	2,213	9,503
Increase (decrease) in other payables and accrued expenses	(989)	(8,300)	4,210
Increase (decrease) in employee benefit liabilities, net	43	76	133
Increase (decrease) in long-term lease liability	(577)
Increase (decrease) in other long-term liabilities	(1,247)	(800)	9,370
Net cash provided by (used in) operating activities	(4,315)	(16,824)	(1,865)
Cash flows from investing activities:
Purchase of property and equipment	(860)	(737)	(2,916)
Purchase of field equipment	(1,465)	(1,370)	(3,795)
Proceeds from maturity of short-term investments	105,661	45,000	255,000
Purchase of short-term investments	(104,325)	(44,750)	(253,782)
Net cash provided by (used in) investing activities	(989)	(1,857)	(5,493)
Cash flows from financing activities:
Proceeds from issuance of shares, net			1,835
Proceeds from long-term loan, net		149,150	149,150
Repayment of long-term loan		(100,000)	(100,000)
Repayment of other long-term loan	(8)	(17)	(84)
Exercise of options and warrants	16,978	2,581	18,468
Net cash provided by (used in) financing activities	16,970	51,714	69,369
Effect of exchange rate changes on cash and cash equivalents	(261)	10	27
Increase (decrease) in cash, cash equivalents and restricted cash	11,405	33,043	62,038
Cash, cash equivalents and restricted cash at beginning of period	142,756	80,718	80,718
Cash, cash equivalents and restricted cash at the end of the period	154,161	113,761	142,756
Cash paid during the period for:
Income taxes	3,033	3,758	20,350
Interest	3,379	$ 3,009	$ 13,334
Non-cash activities upon implementation of ASC-842:
Right of use assets obtained in exchange for lease obligations:	$ 15,733