Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating activities
Net loss	$ (28,812)	$ (69,445)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of premium on marketable securities	246	265
Amortization of debt discount and issuance cost	275	130
Depreciation	173	28
Non-cash in-process research and development		53,029
Stock-based compensation	4,432	2,911
Changes in assets and liabilities:
Prepaid expenses and other current assets	220	(1,767)
Restricted cash		3,888
Other assets	7
Accounts payable and other accrued liabilities	1,616	(1,906)
Deferred development funds		(2,147)
Other liabilities	(15)	(2)
Net cash used in operating activities	(21,858)	(15,016)
Investing activities
Purchases of marketable securities		(9,605)
Proceeds from sales of marketable securities	1,929	279
Proceeds from maturities of marketable securities	22,500	6,375
Investment in property and equipment	(268)	(42)
Net cash provided by (used in) investing activities	24,161	(2,993)
Financing activities
Repayment of notes payable	(1,546)	(1,420)
Proceeds from public offering, net of issuance costs	134,973
Proceeds from common stock option exercises	914	1,080
Net cash provided by (used in) financing activities	134,341	(340)
Net increase (decrease) in cash and cash equivalents	136,644	(18,349)
Cash and cash equivalents at beginning of period	29,226	111,518
Cash and cash equivalents at end of period	165,870	93,169
Supplemental disclosures
Issuance of common stock to Bayer		31,429
Note payable issued to Bayer at fair value		$ 21,600