CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net loss	$ (36,185)	$ (43,975)
Non-cash adjustments reconciling net loss to operating cash flows:
Depreciation	91	101
Amortization of premium on investments	(178)	25
Share-based compensation expense	3,989	5,326
Changes in operating assets and liabilities:
Other current assets	(2,054)	1,349
Other long-term assets	(1,605)	395
Accounts payable, accrued liabilities and other long-term liabilities	(3,117)	3,973
Cash flows used in operating activities	(35,849)	(33,596)
Investing activities:
Purchases of short-term investments	(86,424)	(49,680)
Disposal and maturities of short-term investments	53,038	55,778
Purchases of property and equipment	(80)	(45)
Cash flows provided by, (used in) investing activities	(33,466)	6,053
Financing activities:
Proceeds from sale of common stock, net	66,816	0
Proceeds from exercise of common stock options and warrants	0	2,355
Proceeds from stock issuances under employee stock purchase plan	71	237
Cash flows provided by financing activities	66,887	2,592
Decrease in cash and cash equivalents	(2,428)	(24,951)
Cash and cash equivalents, beginning of period	22,383	49,493
Cash and cash equivalents, end of period	$ 19,955	$ 24,542