Unaudited Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net loss	$ (15,312)	$ (15,881)
Adjustments to reconcile net loss to net cash used in operating activities:
Impairment loss on classification of assets as held for sale	0	1,350
Depreciation	7	447
Stock-based compensation expense	616	1,115
Write off of deferred offering costs	111	0
Change in fair value of warrant liability	(101)	0
Changes in deferred rent	0	(122)
Changes in operating assets and liabilities:
Accounts receivable and unbilled services	0	(214)
Prepaid expenses, other assets, and deferred costs	(1,003)	(1,262)
Accounts payable and accrued expenses	278	467
Accrued severance and retention cost obligations	(2,419)	1,499
Deferred revenue	(128)	(218)
Net cash used in operating activities	(17,951)	(12,819)
Cash flows from investing activities:
Purchases of property and equipment	(14)	(527)
Purchase of short-term investments	(12,472)	0
Net cash used in investing activities	(12,486)	(527)
Cash flows from financing activities:
Proceeds from public offerings	22,500	41,400
Payments of deferred offering costs and underwriting discounts and commissions	(1,746)	(3,335)
Proceeds from Sales Agreement	558	0
Proceeds from employee stock purchase plan issuance	5	95
Net cash provided by financing activities	21,317	38,160
Net decrease in cash and cash equivalents	(9,120)	24,814
Cash and cash equivalents, beginning of period	46,985	32,243
Cash and cash equivalents, end of period	37,865	57,057
Supplemental cash flow information:
Cash received for interest	67	0
Noncash financing and investing activities:
Deferred offering costs included in accounts payable and accrued expenses	205	53
Equipment purchases in accounts payable and accrued expenses	0	20
Deferred offering costs reclassified to additional-paid-in capital	$ 65	$ 3,388