CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (64,544)	$ (43,698)	$ (52,859)
Non-cash adjustments reconciling net loss to operating cash flows
Depreciation of property and equipment	212	199	171
Amortization of premium on investments	337	534	0
Share-based compensation expense	10,254	7,050	1,823
Loss on disposal of property and equipment	0	0	40
Change in lease incentive liability	0	0	(70)
Change in fair value of warrant liability	0	4,517	19,799
Change in fair value adjustment of share-based compensation liability	0	0	1,369
Change in restructuring costs	0	13	0
Changes in operating assets and liabilities
Other current assets	279	(1,209)	340
Other long-term assets	(1,675)	(326)	0
Accounts payable and accrued liabilities	4,370	151	(68)
Other current and long term liabilities	53	21	0
Cash flows used in operating activities	(50,714)	(32,748)	(29,455)
Investing activities:
Purchases of short-term investments	(104,954)	(10,468)	(68,408)
Disposal and maturities of short-term investments	54,530	35,073	39,138
Purchases of property and equipment	(329)	(386)	(204)
Proceeds from disposal of property and equipment	0	0	4
Cash flows (used in) provided by investing activities	(50,753)	24,219	(29,470)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	143,293	0	54,196
Proceeds from issuance under employee stock purchase plan	522	0	0
Proceeds from exercise of common stock options and warrants	552	887	561
Cash flows provided by financing activities	144,367	887	54,757
Increase (decrease) in cash and cash equivalents	42,900	(7,642)	(4,168)
Cash and cash equivalents, beginning of year	6,593	14,235	18,403
Cash and cash equivalents, end of year	49,493	6,593	14,235
Income taxes paid	0	0	35
Net exercise of warrants	$ 0	$ 993	$ 2,586