CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities:
Net loss	$ (21,914)	$ (11,940)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation of property and equipment	58	44
Amortization of premium on investments	14	99
Share-based compensation expense	3,038	2,316
Changes in operating assets and liabilities:
Other current assets	843	188
Accounts payable, accrued liabilities and other long-term liabilities	1,009	(482)
Cash flows used for operating activities	(16,952)	(9,775)
Investing activities:
Purchases of property and equipment	(45)	(18)
Purchases of short-term investments	(21,797)	(35,979)
Disposal and maturities of short-term investments	21,530	4,880
Cash flows used by investing activities	(312)	(31,117)
Financing activities:
Proceeds from sale of common stock, net	0	48,361
Proceeds from exercise of warrants and common stock options	2,326	245
Cash flows provided by financing activities	2,326	48,606
(Decrease) increase in cash and cash equivalents	(14,938)	7,714
Cash and cash equivalents, beginning of period	49,493
Cash and cash equivalents, end of period	34,555
Fixed asset additions included within accounts payable	$ 0	$ 197