CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities:
Net loss	$ (14,709)	$ (17,846)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation	41	45
Amortization of premium on investments	(162)	(71)
Share-based compensation expense	3,660	1,766
Changes in operating assets and liabilities:
Other current assets	502	704
Other long-term assets	25	(710)
Accounts payable, accrued liabilities, deferred revenue and other liabilities	2,745	(3,540)
Cash flows used in operating activities	(7,948)	(18,232)
Investing activities:
Purchases of short-term investments	(102,820)	(63,310)
Disposal and maturities of short-term investments	17,742	22,100
Cash flows used in investing activities	(85,078)	(41,210)
Financing activities:
Proceeds from sale of common stock, net	0	66,816
Proceeds from exercise of common stock options and warrants	5,890	0
Cash flows provided by financing activities	5,890	66,816
Decrease in cash and cash equivalents	(87,136)	7,374
Cash and cash equivalents, beginning of period	107,703	22,383
Cash and cash equivalents, end of period	20,567	29,757
Supplemental disclosures of non-cash investing activities:
Fixed asset additions included within accounts payable	$ 0	$ 54