Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 754	$ 6,937
MedImmune upfront payment received	5,000
Collaborators [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	22	6,125
Royalties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	730	781
Research grants [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	0	12
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 2	$ 19