CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' DEFICIT - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Treasury Stock [Member]	Other Comprehensive Income (Loss)	Total
Balance beginning at Dec. 31, 2017	$ 162,000	$ 1,023,532,000	$ (1,114,359,000)	$ (2,450,000)	$ (8,617,000)	$ (101,732,000)
Balance beginning (in shares) at Dec. 31, 2017	16,184,241
Balance ending at Mar. 31, 2018	$ 174,000	1,072,689,000	(1,160,711,000)	(2,450,000)	(9,071,000)	(99,369,000)
Balance ending (in shares) at Mar. 31, 2018	17,360,221
Balance beginning at Dec. 31, 2017	$ 162,000	1,023,532,000	(1,114,359,000)	(2,450,000)	(8,617,000)	(101,732,000)
Balance beginning (in shares) at Dec. 31, 2017	16,184,241
Non-cash compensation cost for stock options, RSUs, ESPP and restricted stock	$ 0	9,497,000	0	0	0	9,497,000
Exercise of stock options/Purchases under ESPP	$ 1,000	1,441,000	0	0	0	1,442,000
Exercise of stock options/Purchases under ESPP, shares	59,736
Restricted stock cancelled	$ 0	0	0	0	0	0
Restricted stock cancelled, in shares	(938)
Issuance of common stock, net of issuance costs	$ 28,000	96,458,000	0	0	0	96,486,000
Issuance of common stock, net of issuance costs, in shares	2,863,932
Unrealized gain on marketable securities	$ 0	0	0	0	22,000	22,000
Foreign currency translation adjustment	0	0	0	0	(2,578,000)	(2,578,000)
Net loss	0	0	(90,844,000)	0	0	(90,844,000)
Balance ending at Jun. 30, 2018	$ 191,000	1,130,928,000	(1,205,203,000)	(2,450,000)	(11,173,000)	(87,707,000)
Balance ending (in shares) at Jun. 30, 2018	19,106,971
Balance beginning at Dec. 31, 2017	$ 162,000	1,023,532,000	(1,114,359,000)	(2,450,000)	(8,617,000)	(101,732,000)
Balance beginning (in shares) at Dec. 31, 2017	16,184,241
Balance ending at Dec. 31, 2018	$ 192,000	1,144,621,000	(1,299,107,000)	(2,450,000)	(11,191,000)	(167,935,000)
Balance ending (in shares) at Dec. 31, 2018	19,245,302
Balance beginning at Mar. 31, 2018	$ 174,000	1,072,689,000	(1,160,711,000)	(2,450,000)	(9,071,000)	(99,369,000)
Balance beginning (in shares) at Mar. 31, 2018	17,360,221
Non-cash compensation cost for stock options, RSUs, ESPP and restricted stock	$ 0	4,252,000	0	0	0	4,252,000
Exercise of stock options/Purchases under ESPP	$ 0	117,000	0	0	0	117,000
Exercise of stock options/Purchases under ESPP, shares	4,325
Issuance of common stock, net of issuance costs	$ 17,000	53,870,000	0	0	0	53,887,000
Issuance of common stock, net of issuance costs, in shares	1,742,425
Unrealized gain on marketable securities	$ 0	0	0	0	14,000	14,000
Foreign currency translation adjustment	0	0	0	0	(2,116,000)	(2,116,000)
Net loss	0	0	(44,492,000)	0	0	(44,492,000)
Balance ending at Jun. 30, 2018	$ 191,000	1,130,928,000	(1,205,203,000)	(2,450,000)	(11,173,000)	(87,707,000)
Balance ending (in shares) at Jun. 30, 2018	19,106,971
Balance beginning at Dec. 31, 2018	$ 192,000	1,144,621,000	(1,299,107,000)	(2,450,000)	(11,191,000)	(167,935,000)
Balance beginning (in shares) at Dec. 31, 2018	19,245,302
Balance ending at Mar. 31, 2019	$ 235,000	1,206,317,000	(1,342,325,000)	(2,450,000)	(12,360,000)	(150,583,000)
Balance ending (in shares) at Mar. 31, 2019	23,495,466
Balance beginning at Dec. 31, 2018	$ 192,000	1,144,621,000	(1,299,107,000)	(2,450,000)	(11,191,000)	(167,935,000)
Balance beginning (in shares) at Dec. 31, 2018	19,245,302
Non-cash compensation cost for stock options, RSUs, ESPP and restricted stock	$ 0	10,179,000	0	0	0	10,179,000
Fractional shares purchased in stock split	0	0	0	(1,000)	0	(1,000)
Exercise of stock options/Purchases under ESPP	$ 1,000	941,000	0	0	0	942,000
Exercise of stock options/Purchases under ESPP, shares	51,388
Issuance of common stock, net of issuance costs	$ 42,000	55,200,000	0	0	0	55,242,000
Issuance of common stock, net of issuance costs, in shares	4,198,776
Unrealized gain on marketable securities	$ 0	0	0	0	5,000	5,000
Foreign currency translation adjustment	0	0	0	0	(1,104,000)	(1,104,000)
Net loss	0	0	(82,821,000)	0	0	(82,821,000)
Balance ending at Jun. 30, 2019	$ 235,000	1,210,941,000	(1,381,928,000)	(2,451,000)	(12,290,000)	(185,493,000)
Balance ending (in shares) at Jun. 30, 2019	23,495,466
Balance beginning at Mar. 31, 2019	$ 235,000	1,206,317,000	(1,342,325,000)	(2,450,000)	(12,360,000)	(150,583,000)
Balance beginning (in shares) at Mar. 31, 2019	23,495,466
Non-cash compensation cost for stock options, RSUs, ESPP and restricted stock	$ 0	4,621,000	0	0	0	4,621,000
Fractional shares purchased in stock split	0	0	0	(1,000)	0	(1,000)
Issuance of common stock, net of issuance costs	$ 0	3,000	0	0	0	3,000
Issuance of common stock, net of issuance costs, in shares	0
Foreign currency translation adjustment	$ 0	0	0	0	70,000	70,000
Net loss	0	0	(39,603,000)	0	0	(39,603,000)
Balance ending at Jun. 30, 2019	$ 235,000	$ 1,210,941,000	$ (1,381,928,000)	$ (2,451,000)	$ (12,290,000)	$ (185,493,000)
Balance ending (in shares) at Jun. 30, 2019	23,495,466