Condensed Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (23,297,000)	$ (16,291,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of preferred stock warrant liabilities	9,956,000	496,000
Stock-based compensation	600,000	81,000
Depreciation and amortization	39,000	1,000
Impairment on short-term investments	10,000
Deferred income taxes	(1,000)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(196,000)	(33,000)
Accrued liabilities	216,000	3,000
Accounts payable	438,000	811,000
Net cash used in operating activities	(12,235,000)	(14,932,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of short-term investments	(18,000)
Change in restricted cash	(150,000)
Purchase of property and equipment	(254,000)	(12,000)
Net cash used in investing activities	(422,000)	(12,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		57,545,000
Repayment of stock subscription receivable		1,159,000
Proceeds from exercise of redeemable convertible preferred stock warrants	267,000
Proceeds from exercise of common stock options	15,000	39,000
Proceeds from early exercise of stock options	13,000
Payment of deferred offering costs	(992,000)	(148,000)
Net cash provided by (used in) financing activities	(697,000)	58,595,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(13,354,000)	43,651,000
CASH AND CASH EQUIVALENTS - Beginning of period	29,154,000	2,429,000
CASH AND CASH EQUIVALENTS - End of period	15,800,000	46,080,000
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	3,000
Cash paid for interest	0	0
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Change in redemption value of redeemable convertible preferred stock	(151,885,000)	(39,275,000)
Issuance of redeemable convertible preferred stock on exercise of warrants	1,125,000
Deferred offering costs included in accounts payable and accrued liabilities	1,744,000	37,000
Property and equipment purchases included in accounts payable	$ 7,000	7,000
Series C Redeemable Convertible Preferred Stock [Member]
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Conversion of long-term note payable and accrued interest into Series C redeemable convertible preferred stock		$ 433,000