Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 102,724	$ 160,754
Marketable securities	321,212	380,560
Collaboration receivable – related party	2,448	4,886
Royalty receivable – related party	1,222	0
Tenant improvement and other receivables	169	3,428
Prepaid expenses and other current assets	17,486	10,264
Total current assets	445,261	559,892
Marketable securities	143,814	32,250
Property and equipment, net	24,431	25,337
Other non-current assets	891	1,615
Total assets	614,397	619,094
Current liabilities:
Accounts payable	22,767	17,106
Accrued expenses	34,031	32,002
Deferred revenue – related party	37,842	35,913
Deferred rent	301	3,412
Total current liabilities	94,941	88,433
Deferred revenue, net of current portion – related party	125,798	154,297
Deferred rent, net of current portion	18,155	17,773
Total liabilities	238,894	260,503
Commitments and contingent liabilities (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized, no shares issued and outstanding at December 31, 2017 and 2016	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized and 48,826,153 and 42,220,444 shares issued and outstanding at December 31, 2017 and 2016, respectively	49	42
Additional paid-in capital	1,174,904	842,013
Accumulated other comprehensive loss	(1,389)	(313)
Accumulated deficit	(798,061)	(483,151)
Total stockholders’ equity	375,503	358,591
Total liabilities and stockholders’ equity	$ 614,397	$ 619,094