CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ 1,930	$ (11,694)	$ (11,490)	$ (47,928)	$ (63,559)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	1,932	2,311	5,993	6,801	9,006
Asset write-downs and impairment of field equipment	78	178	239	320	407
Amortization of discount (premium)	(547)	(555)	(1,712)	1,502	1,022
Share-based compensation to employees	14,338	10,479	37,719	29,205	39,846
Decrease (increase) in accounts receivables	(9,986)	3,577	(17,020)	(4,805)	(10,325)
Decrease (increase) in inventories	1,067	(1,735)	(1,832)	385	(529)
Increase (decrease) in accounts payable and accrued expenses	6,433	2,839	10,902	(2,760)	13,713
Decrease (increase) in other long-term assets	1,069	155	1,151	(743)	(949)
Increase (decrease) in other long-term liabilities	(1,407)	83	(4,292)	(656)	9,503
Net cash provided by (used in) operating activities	14,907	5,638	19,658	(18,679)	(1,865)
Cash flows from investing activities:
Purchase of property, equipment and field equipment	(2,708)	(1,353)	(7,430)	(4,918)	(6,711)
Proceeds from maturity of short-term investments	105,000	45,000	315,661	150,000	255,000
Purchase of short-term investments	(104,466)	(44,652)	(313,142)	(148,786)	(253,782)
Net cash provided by (used in) investing activities	(2,174)	(1,005)	(4,911)	(3,704)	(5,493)
Cash flows from financing activities:
Proceeds from issuance of shares, net	0	0	1,208	938	1,835
Proceeds from long-term loan, net	0	0	0	149,150	149,150
Repayment of long-term loan	(7)	(22)	(23)	(100,063)	(100,084)
Exercise of options and warrants	15,475	3,924	51,910	16,779	18,468
Net cash provided by (used in) financing activities	15,468	3,902	53,095	66,804	69,369
Effect of foreign currency translation	(216)	(2)	(430)	19	27
Increase (decrease) in cash, cash equivalents and restricted cash	27,985	8,533	67,412	44,440	62,038
Cash, cash equivalents and restricted cash at the beginning of the period	182,183	116,625	142,756	80,718	80,718
Cash, cash equivalents and restricted cash at the end of the period	210,168	125,158	210,168	125,158	142,756
Cash paid during the period for:
Income taxes	3,040	4,145	10,431	16,159	20,350
Interest	3,453	3,454	10,247	9,879	13,334
Non-cash activities in accordance with of ASC-842:
Right-of-use assets obtained in exchange for lease obligations	$ 1,062	$ 0	$ 18,335	$ 0	$ 0