Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 1,250	$ 6,937
MedImmune upfront payment received	5,000
Collaborators [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	60	6,125
Royalties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	1,185	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	$ 5	$ 19