CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (22,373)	$ (26,144)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	492	675
Amortization of deferred financing costs	112	120
Amortization of deferred compensation for services	89	76
Amortization of premium on investment securities	(138)	(301)
Non-cash lease expense	502	439
Stock-based compensation	2,948	1,922
Change in derivative liabilities	82	37
Non-cash interest associated with debt discount accretion	127	113
Changes in operating assets and liabilities:
Unbilled revenue		5,000
Prepaid expenses and other assets	(928)	411
Accounts payable	(1,174)	777
Accrued compensation and benefits	(2,502)	(1,089)
Lease liabilities	(614)
Accrued and other liabilities	(394)	1,051
Deferred revenue	(1,175)
Net cash used in operating activities	(24,946)	(16,913)
Investing activities
Proceeds from maturities of investments	4,000	55,020
Purchases of investments	(54,858)	(24,874)
Purchases of property and equipment	(25)	(165)
Net cash (used in) provided by investing activities	(50,883)	29,981
Financing activities
Proceeds from issuance of common stock under stock plans	375	198
Issuance of common stock upon exercise of options	216	2
Net cash provided by financing activities	591	200
Net (decrease) increase in cash and cash equivalents	(75,238)	13,268
Cash and cash equivalents at beginning of period	181,133	78,768
Cash and cash equivalents at end of period	$ 105,895	92,036
Supplementary disclosure of cash flow information:
Income taxes paid		2
Supplementary disclosure of non-cash activities:
Right-of-use assets obtained in exchange for lease obligations		$ 5,810