Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 277,486	$ 237,677
Collaboration receivables (all amounts are with a related party)	8,435	8,547
Prepaid expenses and other current assets	9,284	10,000
Short-term investments	136,954	193,692
Total current assets	432,159	449,916
Property and equipment, net	6,668	6,812
Operating lease - right of use asset, net	22,531	23,908
Other assets	1,681	1,793
Long-term investments	1,123	22,477
Total assets	464,162	504,906
Current liabilities:
Accounts payable	3,929	2,295
Accrued expenses	18,189	24,895
Operating lease liability - right of use	6,412	6,183
Total current liabilities	28,530	33,373
Operating lease liability - right of use, net of current portion	18,506	20,201
Warrants to purchase common stock	3,304	1,856
Total liabilities	50,340	55,430
Commitments and contingencies (Note 13)
Stockholders’ equity:
Undesignated preferred stock, $0.001 par value: 25,000,000 shares authorized and no shares issued or outstanding	0	0
Common stock, $0.001 par value: 175,000,000 shares authorized; 53,519,920 and 53,123,567 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	53	53
Additional paid-in capital	1,176,359	1,160,807
Accumulated deficit	(762,346)	(711,407)
Accumulated other comprehensive (loss) income	(244)	23
Total stockholders’ equity	413,822	449,476
Total liabilities and stockholders’ equity	$ 464,162	$ 504,906