Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 105,372	$ 120,738
Prepaid expenses and other current assets	4,015	5,536
Income tax receivable	353	339
Other receivables	458	459
Total current assets	110,198	127,072
Property and equipment, net	3,314	3,727
Right-of-use asset	7,159	0
Income tax receivable	140	140
Total non-current assets	10,613	3,867
Total assets	120,811	130,939
Current liabilities:
Accounts payable	689	555
Accrued expenses	7,235	8,139
Current portion of deferred rent	0	92
Current portion of lease liability	641	0
Current portion of notes payable	63	61
Total current liabilities	8,628	8,847
Long-term liabilities:
Royalty obligation payable to Iowa Economic Development Authority	6,000	6,000
Notes payable	11	43
Lease liability	7,485	0
Deferred rent	0	906
Total long-term liabilities	13,496	6,949
Total liabilities	22,124	15,796
Stockholders' equity:
Blank check preferred stock, $0.01 par value: Authorized shares — 5,000,000 at June 30, 2019 and December 31, 2018; issued and outstanding shares — 0 at June 30, 2019 and December 31, 2018	0	0
Common stock, $0.01 par value: Authorized shares — 75,000,000 at June 30, 2019 and December 31, 2018; issued 37,413,093 and 37,343,547 at June 30, 2019 and December 31, 2018, respectively; and outstanding 37,300,960 and 37,251,220 at June 30, 2019 and December 31, 2018, respectively	373	373
Additional paid-in capital	410,946	407,199
Treasury stock, at cost: 112,133 and 92,327 shares at June 30, 2019 and December 31, 2018, respectively	(1,450)	(1,417)
Accumulated deficit	(311,182)	(291,012)
Total stockholders' equity	98,687	115,143
Total liabilities and stockholders' equity	$ 120,811	$ 130,939