Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 109,534	$ 50,312
Marketable securities	474,114	479,470
Equity securities	2,611
Accounts receivable	8,925	21,574
Income tax receivable	804	502
Prepaid expenses and other current assets	7,398	6,547
Total current assets	603,386	558,405
Property and equipment, net	16,239	15,805
Patents, licenses, and other intangible assets, net	15,162	14,421
Marketable securities - long term	1,145	71,526
Income tax receivable		402
Other assets	8,788	9,691
Total assets	644,720	670,250
Current liabilities
Accounts payable	10,513	10,189
Accrued expenses	9,157	8,995
Lease liabilities	2,094	2,169
Deferred revenue	44,685	45,205
Total current liabilities	66,449	66,558
Lease liabilities, net of current portion	7,626	8,565
Deferred revenue, net of current portion		1,926
Total liabilities	74,075	77,049
Commitments and contingencies
Stockholders' equity
Preferred stock, $0.01 par value: 10,000,000 authorized shares; -0- issued and outstanding shares at June, 2020 and December 31, 2019
Common stock, $0.01 par value: 200,000,000 authorized shares at June 30, 2020 and December 31, 2019; 57,214,253 issued and outstanding at June 30, 2020 and 56,902,301 issued and outstanding at December 31, 2019	572	569
Additional paid-in capital	908,084	887,873
Accumulated other comprehensive income	1,483	1,161
Accumulated deficit	(339,494)	(296,402)
Total stockholders' equity	570,645	593,201
Total liabilities and stockholders' equity	$ 644,720	$ 670,250