CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (163,357)	$ (152,598)
Adjustments to reconcile net loss to net cash used in operating activities:
Changes in fair value of warrant liabilities	0	49,026
Depreciation and amortization	1,839	670
Interest on non-recourse debt	20,373	19,790
Amortization of deferred revenue	0	13
Amortization of bond premiums	0	36
Amortization of debt issuance costs	25	73
Amortization of deferred rent	0	218
Right-of-use asset amortization	130	0
Decrease in allowance for doubtful accounts	0	(13)
Non-cash expense related to stock-based compensation	4,147	2,682
Changes in deferred revenue	65,000	0
Changes in other operating assets and liabilities	4,670	10,456
Net cash used in operating activities	(67,173)	(69,647)
Cash flows from investing activities
Purchases of marketable securities	0	(135)
Proceeds from sales/maturities of marketable securities	0	52,150
Purchases of property and equipment	(5,699)	(7,985)
Net cash (used in) provided by investing activities	(5,699)	44,030
Cash flows from financing activities:
Exercise of stock options, net	2,106	1,596
Exercise of warrants	0	27,750
Proceeds from the issuance of common stock in at-the-market offering	5,829	0
Proceeds from the issuance of non-recourse debt	0	182,216
Debt conversion fees	0	(3)
Tax withholding payments for stock-based compensation	0	(1,472)
Net cash provided by financing activities	7,935	577,338
Effect of changes in exchange rates on cash, cash equivalents and restricted cash	(14)	(99)
Net (decrease) increase in cash, cash equivalents and restricted cash	(64,951)	551,622
Cash, cash equivalents and restricted cash beginning of period	494,173	60,960
Cash, cash equivalents and restricted cash end of period	429,222	612,582
Supplemental disclosure of cash flow information:
Interest paid	169	475
Schedule for non-cash investing and financing activities:
Non-cash component of warrant exercise	0	137,979
Accrued capital expenditures	404	2,173
Shares received in cashless exercise	1,272	0
Total cash, cash equivalents and restricted cash	494,173	60,960
Private placement
Cash flows from financing activities:
Proceeds from private offering of common stock	0	67,784
Public offering
Cash flows from financing activities:
Proceeds from private offering of common stock	$ 0	$ 299,467