CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net (loss) income	$ (29,029)	$ 1,891	$ (33,452)
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Depreciation and amortization	285	178	366
Non-cash interest expense	0	26	108
Stock-based compensation expense	1,381	4,013	2,529
Change in fair value of warrant liability	(5)	(110)	(3,104)
Loss (gain) from change in fair value of contingent consideration	9,100	(1,100)	0
Loss on extinguishment of debt	0	221	0
Gain on sale of equipment	(108)	(24)	0
Changes in operating assets and liabilities:
Prepaid expenses and other assets	164	800	110
Restricted cash	0	84	0
Accounts payable	(760)	(742)	(1,212)
Accrued expenses and other liabilities	1,746	(1,936)	226
Deferred revenue	(425)	19	(100)
Due to related party	(114)	(698)	0
Net cash (used in) provided by operating activities	(17,765)	2,622	(34,529)
Investing activities
Cash acquired in acquisition	0	136	0
Net sales (purchases) of property and equipment	98	325	(287)
Net cash provided by (used in) investing activities	98	461	(287)
Financing activities
Proceeds from issuance of notes payable, net of debt issuance costs	0	0	5,000
Payments on equipment financing and notes payable	0	(14,124)	(877)
Proceeds from issuance of common stock and common stock warrants, net of issuance costs	6,908	0	12,650
Proceeds from exercise of common stock options and common stock warrants	85	269	63
Proceeds from sale of common stock pursuant to ESPP	12	35	0
Net cash provided by (used in) financing activities	7,005	(13,820)	16,836
Net decrease in cash and cash equivalents	(10,662)	(10,737)	(17,980)
Cash and cash equivalents at beginning of period	25,342	36,079	54,059
Cash and cash equivalents at end of period	14,680	25,342	36,079
Supplemental non-cash investing and financing activities
Common stock issued in connection with the acquisition (Note 3)	0	13,525	0
Fair value of assets acquired in the acquisition, excluding cash	0	79,366	0
Fair value of liabilities assumed in the acquisition	0	19,777	0
Adjustment to fair value of assets acquired and liabilities assumed during provisional period (Note 3)	14,600	0	0
Issuance of warrants to purchase common stock	2,679	0	328
Supplemental cash flow information
Cash paid for interest	$ 0	$ 663	$ 930