Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 132,741	$ 160,754
Marketable securities	375,187	380,560
Collaboration receivable – related party	3,489	4,886
Royalty receivable – related party	715	0
Tenant improvement and other receivables	859	3,428
Prepaid expenses and other current assets	15,316	10,264
Total current assets	528,307	559,892
Marketable securities	133,804	32,250
Property and equipment, net	24,019	25,337
Other non-current assets	1,070	1,615
Total assets	687,200	619,094
Current liabilities:
Accounts payable	17,899	17,106
Accrued expenses	30,760	32,002
Deferred revenue – related party	35,867	35,913
Deferred rent	3,586	3,412
Total current liabilities	88,112	88,433
Deferred revenue, net of current portion – related party	134,202	154,297
Deferred rent, net of current portion	15,080	17,773
Total liabilities	237,394	260,503
Stockholders’ equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized; no shares issued or outstanding at September 30, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized; 48,617,989 and 42,220,444 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	49	42
Additional paid-in capital	1,160,048	842,013
Accumulated other comprehensive loss	(515)	(313)
Accumulated deficit	(709,776)	(483,151)
Total stockholders’ equity	449,806	358,591
Total liabilities and stockholders’ equity	$ 687,200	$ 619,094