Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (66,374)	$ (45,498)	$ (30,933)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	2,340	1,782	817
Amortization of intangible assets	11	10	71
Amortization of investment discount	374	188	269
Equity-based compensation	8,775	8,388	9,624
Impairment loss	0	0	3
Realized gain on available-for-sale securities	(6)	0	0
Loss on disposal of property & equipment	23	0	0
(Increase) decrease in assets:
Accounts receivable	43	1	(54)
Prepaid expense and other	1,292	(1,241)	(166)
Other current assets	(171)	(12)	0
Increase (decrease) in liabilities:
Accounts payable	(1,242)	329	1,336
Accrued liabilities	1,619	827	80
Deferred revenue and income	(92)	100	168
Net cash used in operating activities	(53,408)	(35,126)	(18,785)
Cash flows from investing activities:
Purchases of equipment	(2,409)	(3,656)	(1,933)
Purchase of available-for-sale securities	(74,075)	(12,418)	(7,657)
Sales of available-for-sale securities	9,716	141	861
Maturity of available-for-sale securities	17,200	13,258	5,357
Net cash used in investing activities	(49,568)	(2,675)	(3,372)
Cash flows from financing activities:
Exercise of warrants and options	1,497	805	923
Common stock issuance cost	(814)	0	0
Issuance of common stock and warrants	226	104,165	44,875
Recovery of related party short-swing profits	866	0	0
Payments on capital lease obligations	(13)	(147)	(107)
Net cash provided by financing activities	1,762	104,823	45,691
Effect of exchange rate on cash	(127)	0	0
Increase (decrease) in cash and cash equivalents	(101,341)	67,022	23,534
Cash and cash equivalents, beginning of period	120,585	53,563	30,029
Cash and cash equivalents, end of period	$ 19,244	$ 120,585	$ 53,563