Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (59,006)	$ (51,153)	$ (62,428)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,197	2,449	2,940
Amortization of operating lease right-of-use assets	1,445
Stock-based compensation expense	5,458	9,897	4,790
Non-cash interest expense	2,407	2,216	2,710
Impairment of property and equipment		683	2,571
(Gain) loss on disposal of property and equipment	(3)	26
Change in fair value of derivative instrument	283	(96)	2,238
Deferred rent		(217)	(115)
Changes in operating assets and liabilities:
Accounts receivable	(1,039)	(1,319)	(140)
Prepaid expenses and other assets	(98)	(570)	125
Inventories, net	(914)	(1,089)	(110)
Accounts payable	2,960	121	(314)
Accrued expenses and other liabilities	3,708	(279)	724
Deferred revenue	(499)	(807)	(709)
Operating lease liabilities	(2,260)
Net cash used in operating activities	(45,361)	(40,138)	(47,718)
Investing activities
Purchases and manufacture of property and equipment	(761)	(593)	(2,476)
Net cash used in investing activities	(761)	(593)	(2,476)
Financing activities
Proceeds from issuance of common stock in public offering, net of offering costs	6,650	49,237	18,640
Proceeds from issuance of shares from employee stock purchase plan and stock option exercises	582	1,967	1,059
Principal repayments of finance leases	(882)	(1,547)	(1,194)
Net cash provided by financing activities	6,350	49,657	18,505
Net increase (decrease) in cash, cash equivalents and restricted cash	(39,772)	8,926	(31,689)
Cash, cash equivalents and restricted cash at beginning of period	50,985	42,059	73,748
Cash, cash equivalents and restricted cash at end of period	11,213	50,985	42,059
Reconciliation of cash, cash equivalents and restricted cash at end of period
Cash and cash equivalents	11,033	50,805	41,799
Restricted cash	180	180	260
Cash, cash equivalents and restricted cash at end of period	11,213	50,985	42,059
Supplemental disclosures of cash flow information
Cash paid for interest	4,659	3,786	3,959
Supplemental disclosures of noncash activities
Transfer of T2 owned instruments and components to inventory	(8)	244	431
Transfer from other liabilities to accrued expenses and other current liabilities	2,400	1,400	585
Right-of-use assets obtained in exchange for new operating lease liabilities	4,805
Change in fair value of warrants issued and modified	924
Purchases of property and equipment included in accounts payable and accrued expenses	$ 107	$ 80	189
Public offering costs unpaid at year end			$ 59