Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (23,410)	$ (23,297)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,666	600
Change in fair value of preferred stock warrant liabilities		9,956
Depreciation and amortization	106	39
Non-cash restructuring charges (note 12)	811
Other	22	9
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	468	(196)
Accrued liabilities	(592)	216
Accounts payable	376	438
Net cash used in operating activities	(19,553)	(12,235)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(193)	(254)
Change in restricted cash	25	(150)
Proceeds from sale of property and equipment	13
Purchase of short-term investments		(18)
Net cash used in investing activities	(155)	(422)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of common stock options	120	15
Payment of deferred offering costs	(15)	(992)
Proceeds from early exercise of stock options		13
Proceeds from exercise of redeemable convertible preferred stock warrants		267
Net cash provided by (used in) financing activities	105	(697)
Effect of foreign exchange rate changes on cash and cash equivalents	(27)
NET DECREASE IN CASH AND CASH EQUIVALENTS	(19,630)	(13,354)
CASH AND CASH EQUIVALENTS - Beginning of period	150,180	29,154
CASH AND CASH EQUIVALENTS - End of period	130,550	15,800
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	80	3
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Change in redemption value of redeemable convertible preferred stock		(151,885)
Issuance of redeemable convertible preferred stock on exercise of warrants		1,125
Deferred offering costs included in accounts payable and accrued liabilities		1,744
Property and equipment purchases included in accounts payable and accrued liabilities	$ 11	$ 7