Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net loss	$ (12,221)	$ (7,032)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,188	230
Depreciation and amortization	30	30
Amortization of debt discount	66	237
Amortization of beneficial conversion feature		24
Noncash interest expense on convertible notes		721
Change in fair value of preferred stock warrant liabilities		(2,036)
Change in assets and liabilities:
Prepaid expenses and other assets	(540)	769
Accounts payable and accrued expenses	1,403	1,093
Deferred rent	(12)	(10)
Net cash used in operating activities	(10,086)	(5,974)
Investing activities
Purchase of property and equipment		(22)
Net cash used in investing activities		(22)
Financing activities
Proceeds from convertible notes, related party		13,000
Payments on capital lease obligations	(6)	(5)
Net cash provided by (used in) financing activities	(6)	12,995
Net increase (decrease) in cash and cash equivalents	(10,092)	6,999
Cash and cash equivalents at beginning of period	62,431	6,178
Cash and cash equivalents at end of period	52,339	13,177
Supplemental disclosure of cash flow information
Cash paid for interest	$ 262	262
Noncash activities:
Financing costs in accrued expenses		$ 38