Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (309,122)	$ (254,234)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	6,124	5,261
Stock-based compensation expense	55,243	55,170
Net accretion of premium and discounts on investments	(2,772)	(2,540)
Loss (gain) on disposal of property and equipment	466	(20)
Non-cash operating lease expense	6,341
Changes in operating assets and liabilities:
Accounts receivable, net	(2,030)	(2,631)
Collaboration receivable – related party	624	(947)
Collaboration receivable – other	(199)	(440)
Royalty receivable – related party	(366)	(641)
Inventory	(4,980)	(863)
Prepaid expenses and other current and non-current assets	(3,552)	1,711
Accounts payable	2,649	(5,830)
Accrued expenses	4,602	(8,537)
Deferred revenue – related party	(25,849)	(15,749)
Operating lease liabilities	(4,190)
Deferred rent	0	56
Net cash used in operating activities	(277,011)	(230,234)
Investing activities
Purchases of marketable securities	(194,822)	(755,368)
Proceeds from maturities and sales of marketable securities	476,382	500,281
Purchases of property and equipment	(5,347)	(5,933)
Net cash provided by (used in) investing activities	276,213	(261,020)
Financing activities
Payment of public offering costs, net of reimbursements	0	(391)
Proceeds from public offering of common stock, net of commissions	0	516,206
Net proceeds from stock option exercises and employee stock purchase plan	12,005	29,193
Net cash provided by financing activities	12,005	545,008
Net change in cash and cash equivalents	11,207	53,754
Cash and cash equivalents at beginning of the period	70,502	102,724
Cash and cash equivalents at end of the period	81,709	156,478
Supplemental disclosure of non-cash investing and financing transactions
Additions to property and equipment in accounts payable and accrued expenses	2,089	501
Proceeds from stock option exercises in other current assets	0	$ 39
Operating lease liabilities arising from obtaining operating lease assets	$ 42,322