Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (26,887)	$ (15,001)	$ (52,739)
Adjustments to reconcile net loss to net cash used in operating activities:
Impairment of property and equipment		232	7,600
Depreciation and amortization	30	9,567	6,219
Net loss (gain) on disposal of fixed assets		253	(127)
Stock-based compensation	999	1,132	2,808
Non-cash interest expense	465	655	347
Non-cash change in fair value of warrant liability	(4,751)
Amortization of premium and discount on investments	14	34	221
Changes in operating assets and liabilities:
Restricted Cash		2,997	598
Accounts receivable	3,614	(2,300)	(1,357)
Tenant improvement allowance receivable			5,833
Prepaid expenses and other current assets	(340)	(116)	1,503
Other noncurrent assets	(827)	96	50
Accounts payable	760	(1,820)	(993)
Accrued clinical trial costs and contract research	2,032	(3,562)	(1,153)
Other accrued liabilities	(609)	(1,627)	(911)
Settlement liability	(4,000)	4,000
Deferred revenue	(1,488)	2,927	(17,623)
Lease exit obligation		(5,206)	4,981
Deferred rent		(10,569)	(9,505)
Other liabilities	(78)	78	0
Net cash used in operating activities	(31,066)	(18,230)	(54,248)
Investing activities
Purchases of marketable securities	(29,421)	(19,085)	(42,306)
Proceeds from maturities and sales of marketable securities	28,664	11,550	109,767
Purchases of property and equipment	(7)	(22)	(12,942)
Proceeds from sale of property and equipment		1,241	191
Net cash (used in) provided by investing activities	(764)	(6,316)	54,710
Financing activities
Proceeds from issuance of common stock and warrants, net of issuance costs	14,846	10,218
Proceeds from issuance of common stock and warrants to related parties	525
Proceeds from issuance of loan payable and warrants	5,000		10,000
Proceeds from issuance of stock for stock-based compensation arrangements	36	268	191
Payments of debt issuance costs	(115)		(1,388)
Principal payments on loans payable		(11,612)	(7,785)
Net cash provided by (used in) financing activities	20,292	(1,126)	1,018
Net (decrease) increase in cash and cash equivalents	(11,538)	(25,672)	1,480
Cash and cash equivalents at beginning of period	26,634	52,306	50,826
Cash and cash equivalents at end of period	15,096	26,634	52,306
Supplemental cash flow information
Cash paid for interest	1,539	$ 1,983	2,018
Non-cash financing activity
Fair value of warrants issued in connection with long term debt	667		$ 413
Fair value of warrants issued in connection with private placement	$ 9,344