Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 283,521	$ 237,677
Collaboration receivables (all amounts are with a related party)	39,752	8,547
Prepaid expenses and other current assets	19,388	10,000
Short-term investments	106,289	193,692
Total current assets	448,950	449,916
Property and equipment, net	7,671	6,812
Operating lease - right of use asset, net	21,116	23,908
Other assets	1,698	1,793
Long-term investments	0	22,477
Total assets	479,435	504,906
Current liabilities:
Accounts payable	12,927	2,295
Accrued expenses	17,966	24,895
Operating lease liability - right of use	6,467	6,183
Total current liabilities	37,360	33,373
Operating lease liability - right of use, net of current portion	16,940	20,201
Warrants to purchase common stock	3,516	1,856
Total liabilities	57,816	55,430
Commitments and contingencies (Note 13)
Stockholders’ equity:
Common stock, $0.001 par value: 175,000,000 shares authorized; 54,166,712 and 53,123,567 shares issued and outstanding at June 30, 2020 and December 31, 2019, respectively	54	53
Additional paid-in capital	1,202,445	1,160,807
Accumulated deficit	(780,797)	(711,407)
Accumulated other comprehensive (loss) income	(83)	23
Total stockholders’ equity	421,619	449,476
Total liabilities and stockholders’ equity	$ 479,435	$ 504,906