Unaudited Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Activities
Net loss	$ (43,122)	$ (36,301)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	808	178
Amortization of premium and discounts on investment securities	98	196
Deferred income taxes	0	23,113
Share-based compensation	6,064	8,332
Changes in operating assets and liabilities:
Due from Novartis Pharma AG	0	(5,673)
Income tax receivable	(52)	(23,076)
Prepaid expense and other current assets	(1,520)	(216)
Accrued interest receivable	74	0
Other assets	459	(11)
Accrued research and development expenses	(19,285)	2,907
Accounts payable and accrued expenses	(3,375)	(4,731)
Deferred revenue	(1,661)	(1,458)
Net cash used in operating activities	(61,512)	(36,740)
Investing Activities
Purchase of marketable securities	(12,014)	(12,005)
Maturities of marketable securities	32,119	10,000
Purchase of property and equipment	0	(62)
Net cash provided by (used in) investing activities	20,105	(2,067)
Financing Activities
Proceeds from stock option/employee stock purchase plan exercises	31	768
Net cash provided by financing activities	31	768
Net change in cash and cash equivalents	(41,376)	(38,039)
Cash and cash equivalents
Beginning of period	133,930	221,861
End of period	92,554	183,822
Supplemental disclosures of non-cash information related to investing activities
Change in unrealized gain (loss) on available for sale securities, net of tax	$ (10)	$ 477