Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net income (loss)	$ (8,074)	$ 80,045
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	1,373	996
Accretion of discount on marketable securities	(573)	(601)
Stock-based compensation	6,512	5,856
Abandonment of capitalized intangible assets	28	58
Equity received in connection with license agreement	(4,589)
Change in fair value of equity security	2,336
Changes in operating assets and liabilities:
Accounts receivable	14,749	(127,489)
Interest receivable	215	31
Prepaid expenses and other assets	71	942
Accounts payable	124	1,689
Accrued expenses	(1,703)	(3,957)
Income taxes		900
Lease liabilities and ROU assets	(54)	(259)
Deferred revenue	(955)	23,061
Net cash provided by (used in) operating activities	9,460	(18,728)
Cash flows from investing activities
Purchase of marketable securities	(142,477)	(49,856)
Purchase of intangible assets	(538)	(1,051)
Purchase of property and equipment	(2,073)	(415)
Proceeds maturities of marketable securities	157,653	64,995
Net cash provided by investing activities	12,565	13,673
Cash flows from financing activities
Proceeds from issuance of common stock upon exercise of stock awards	1,471	667
Net cash provided by financing activities	1,471	667
Net increase in cash and cash equivalents	23,496	(4,388)
Cash and cash equivalents, beginning of period	50,312	26,246
Cash and cash equivalents, end of period	73,808	21,858
Cash paid for:
Interest	6	4
Supplemental disclosures of non-cash investing activities
Net unrealized gain (loss) on marketable securities, net of tax	$ (105)	$ 1,316