Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (112,477)	$ (98,036)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	7,338	13,824
Depreciation and amortization expense	7,175	6,698
Change in fair value of warrant derivative liability	19,192	0
Impairment of intangible assets	2,064	0
Amortization of (discount) premium on investment securities, net	(30)	94
Amortization of right-of-use assets	1,331	0
Accretion of lease liability	804	(276)
Amortization of deferred issuance costs	885	886
Loss on disposition of fixed assets	6	10
Warrant and private placement option issuance costs	3,047	0
Changes in operating assets and liabilities:
Accounts receivable, interest and other receivables	606	(589)
Prepaid expenses and other assets	(1,096)	1,070
Accounts payable	(1,131)	460
Accrued liabilities and other	(2,300)	2,197
Deferred revenue	(2,983)	(1,120)
Net cash used in operating activities	(77,569)	(74,782)
Cash flows from investing activities:
Purchases of investment securities	0	(59,335)
Proceeds from sale of investment securities	49,379	71,362
Purchases of property and equipment	(522)	(1,617)
Cash provided by investing activities	48,857	10,410
Cash flows from financing activities:
Proceeds from issuance of common stock in a public offering, net	8,977	64,860
Proceeds from issuance of redeemable convertible preferred stock in a public offering, net	22,944	0
Proceeds from issuance of warrants in a public offering, net	30,888	0
Proceeds received from private placement option, net	11,152	0
Proceeds from exercise of stock options	76	3,270
Proceeds from issuance of stock from employee stock purchase plan	98	205
Payment on financing lease obligations	(47)	(31)
Payment of issuance costs on common stock	0	(195)
Net cash provided by financing activities	74,088	68,109
Effect of exchange rate changes on cash	(228)	(98)
Net change in cash, cash equivalents and restricted cash	45,148	3,639
Cash, cash equivalents and restricted cash at beginning of period	48,668	45,029
Cash, cash equivalents and restricted cash at end of period	93,816	48,668
Supplemental cash flow information:
Cash paid during the period for interest	3,201	3,025
Non-cash investing and financing activities:
Purchases of property and equipment in accounts payables and accrued liabilities	0	27
Financing leases incurred for equipment	167	0
Conversion of redeemable preferred stock into common stock	1,476	0
Reclassification of property and equipment, net to assets held for sale	$ 12,039	$ 0