CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities:
Net loss	$ (43,975)	$ (27,386)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation	101	100
Amortization of premium on investments	25	251
Share-based compensation expense	5,326	5,108
Changes in operating assets and liabilities:
Other current assets	1,349	1,338
Other long-term assets	395	(38)
Accounts payable, accrued liabilities and other long-term liabilities	3,973	1,737
Cash flows used for operating activities	(33,596)	(18,814)
Investing activities:
Purchases of short-term investments	(49,680)	(41,024)
Disposal and maturities of short-term investments	55,778	17,980
Purchases of property and equipment	(45)	(297)
Cash flows provided (used) by investing activities	6,053	(23,341)
Financing activities:
Proceeds from sale of common stock, net	0	48,361
Proceeds from exercise of warrants and common stock options	2,355	330
Proceeds from stock issuances under employee stock purchase plan	237	250
Cash flows provided by financing activities	2,592	48,941
(Decrease) increase in cash and cash equivalents	(24,951)	6,786
Cash and cash equivalents, beginning of period	49,493	6,593
Cash and cash equivalents, end of period	$ 24,542	$ 13,379