CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ (1,270)	$ (15,510)	$ (13,420)	$ (36,234)	$ (63,559)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	2,132	2,287	4,061	4,490	9,006
Asset write-downs and impairment of field equipment	86	93	161	142	407
Share-based compensation to employees	13,732	10,206	23,381	18,726	39,846
Decrease (increase) in trade receivables	(3,313)	(3,599)	(6,010)	(5,271)	(4,151)
Amortization of discount (premium)	(587)	(370)	(1,165)	2,057	1,022
Decrease (increase) in receivables and prepaid expenses	(1,685)	(1,277)	(1,024)	(3,111)	(6,174)
Decrease (increase) in inventories	(1,316)	482	(2,899)	2,120	(529)
Decrease (increase) in other long-term assets	(632)	(278)	(2,531)	(898)	(949)
Decrease (increase) in right of use assets, net	800		2,613
Increase (decrease) in trade payables	126	1,016	3,361	3,229	9,503
Increase (decrease) in other payables and accrued expenses	2,097	(528)	1,108	(8,828)	4,210
Increase (decrease) in employee benefit liabilities, net	50	1	93	77	133
Increase (decrease) in long-term lease liability	(575)		(1,152)
Increase (decrease) in other long-term liabilities	(579)	(16)	(1,826)	(816)	9,370
Net cash provided by (used in) operating activities	9,066	(7,493)	4,751	(24,317)	(1,865)
Cash flows from investing activities:
Purchase of property and equipment	(892)	(854)	(1,752)	(1,591)	(2,916)
Purchase of field equipment	(1,505)	(604)	(2,970)	(1,974)	(3,795)
Proceeds from maturity of short-term investments	105,000	60,000	210,661	105,000	255,000
Purchase of short-term investments	(104,351)	(59,384)	(208,676)	(104,134)	(253,782)
Net cash provided by (used in) investing activities	(1,748)	(842)	(2,737)	(2,699)	(5,493)
Cash flows from financing activities:
Proceeds from issuance of shares, net	1,208	938	1,208	938	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)	(24)	(16)	(41)	(84)
Exercise of options and warrants	19,457	10,274	36,435	12,855	18,468
Net cash provided by (used in) financing activities	20,657	11,188	37,627	62,902	69,369
Effect of exchange rate changes on cash and cash equivalents	47	11	(214)	21	27
Increase (decrease) in cash, cash equivalents and restricted cash	28,022	2,864	39,427	35,907	62,038
Cash, cash equivalents and restricted cash at beginning of period	154,161	113,761	142,756	80,718	80,718
Cash, cash equivalents and restricted cash at the end of the period	182,183	116,625	182,183	116,625	142,756
Cash paid during the period for:
Income taxes	4,358	8,256	7,391	12,014	20,350
Interest	3,415	$ 3,416	6,794	$ 6,425	$ 13,334
Non-cash activities upon implementation of ASC-842:
Right of use assets obtained in exchange for lease obligations	$ 1,539		$ 17,273