Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating Activities
Net loss	$ (37,334)	$ (41,568)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,707	2,533
Depreciation and amortization	93	112
Changes in operating assets and liabilities:
Accounts receivable	13,445
Prepaid and other assets	225	(477)
Accounts payable	(35)	875
Accrued compensation and other accrued liabilities	2,156	2,944
Operating lease liability and right-of-use asset	45	57
Deferred revenue	(14,236)
Net cash flows used in operating activities	(32,934)	(35,524)
Investing Activities
Proceeds from maturities of short-term investments	74,082	133,967
Purchases of short-term and long-term investments	(91,742)	(106,950)
Purchases of property and equipment	(228)	(65)
Net cash flows (used in) provided by investing activities	(17,888)	26,952
Financing Activities
Issuance of common stock for public offering, net of issuance costs	59,941
Issuance of common stock from stock grants and option exercises	435	327
Net cash flow provided by financing activities	60,376	327
Net increase (decrease) in cash, cash equivalents and restricted cash	9,554	(8,245)
Cash, cash equivalents and restricted cash at beginning of the period	15,369	31,263
Cash, cash equivalents and restricted cash at end of the period	$ 24,923	23,018
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Right-of-use asset and operating lease liability recorded upon the adoption of ASC 842, net		$ 2,052