Unaudited Condensed Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net loss	$ (8,955)	$ (5,128)
Adjustments to reconcile net loss to net cash used for operating activities:
Share-based compensation expense	2,906	2,673
Third party share-based compensation expense	496	0
Issuance of common stock for services	0	25
Depreciation expense	11	2
Changes in operating assets and liabilities:
Prepaid clinical expenses	79	0
Prepaid expenses and other current assets	(485)	(113)
Other assets	(57)	0
Accounts payable	1,729	(272)
Accrued expenses	(809)	75
Accrued payroll and related expenses	(424)	9
Net cash used for operating activities	(5,509)	(2,729)
Investing activities
Purchase of property and equipment	(391)	(15)
Net cash used for investing activities	(391)	(15)
Financing activities
Net proceeds from the exercise of stock options for common stock	57	0
Net cash provided by financing activities	57	0
Net decrease in cash and cash equivalents	(5,843)	(2,744)
Cash and cash equivalents at beginning of period	48,555	8,629
Cash, cash equivalents at end of period	42,712	5,885
Conversion of Series C-1 and D-1 Preferred Stock into Common Stock [Member]
Non-cash investing and financing activity
Conversion of stock	0	1,623
Conversion of Series F Preferred Stock into Common Stock [Member]
Non-cash investing and financing activity
Conversion of stock	$ 61	$ 184