Unaudited Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Operating activities
Net loss	$ (15,592)	$ (8,591)	$ (30,416)	$ (31,685)	$ (24,183)	$ (62,101)	$ (62,101)
Adjustments to reconcile net loss to net cash used for operating activities:
Share-based compensation expense	1,590	2,407	6,321	6,782	3,997
Share-based compensation expense						13,103
Depreciation and amortization expense					1,798	2,263
Loss on disposal of equipment					904	15
Unrealized gains on short-term investments					(63)	0
Non-cash interest expense					3,392	4,678
Non-cash rent expense					699	639
Changes in operating assets and liabilities:
Accounts receivable, net					1,117	(512)
Inventory, net					(909)	52
Prepaid expenses and other current assets					1,675	22
Accounts payable					(1,696)	(3,664)
Accrued expenses					(3,378)	974
Accrued payroll and related expenses					(2,591)	(3,429)
Lease liability					(1,357)	(1,241)
Net cash used for operating activities					(20,595)	(49,201)
Investing activities
Proceeds from the sale of property and equipment					2,860	0
Purchases of property and equipment					0	(441)
Purchases of short-term investments					(2,999)	0
Net cash used for investing activities					(139)	(441)
Financing activities
Net proceeds from issuance of common stock under 2013 Equity Plan					605	0
Net proceeds from issuance of common stock under ESPP					359	484
Net cash provided by financing activities					964	484
Net decrease in cash and restricted cash					(19,770)	(49,158)
Cash and restricted cash at beginning of period		88,729		173,513	88,729	173,513
Cash and restricted cash at end of period	68,959		124,355		68,959	124,355	173,513
Supplemental disclosure of non-cash investing and financing activities:
Conversion of Series F Convertible Preferred Stock into common stock					0	2,737
Cumulative-effect adjustment from adoption of ASU 2018-07								$ 0		$ (160)
Initial recognition of right-of-use lease asset					0	16,798
Reconciliation of cash and restricted cash to the condensed consolidated balance sheets
Cash								68,353	$ 87,820	123,446
Restricted cash								606		909
Total cash and restricted cash	$ 68,959	$ 88,729	$ 124,355	$ 173,513	$ 68,959	$ 124,355	$ 173,513	$ 68,959	$ 88,729	$ 124,355