Summary of Significant Accounting Policies (Tables)

6 Months Ended

12 Months Ended

Jun. 30, 2013

Dec. 31, 2012

Revenue Accounted for 10% or More of Total Revenues

Customers whose collaborative research and development revenue accounted for 10% or more of total revenues were as follows:

	Six Months Ended June 30,
	2012			2013
Novartis AG		100	%		—
Bristol-Myers Squibb Company and Pfizer Inc.		—			54	%
Bayer Pharma, AG and Janssen Pharmaceuticals, Inc.		—			43	%

Customers that accounted for 10% or more of total revenues were as follows:

	Year Ended December 31,
	2010			2011			2012
Merck		76	%		40	%		–
Novartis		24	%		12	%		97	%
Biogen Idec		–			48	%		–