Fair value measurements (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 17, 2014
Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period				$ 25,155
Expense included in earnings				1,263
Settlements				(964)
Purchases, sales and issuances				0
Transfers in/(out) of Level 3				0
Balance, end of period		$ 22,928		22,928
Evolva Holding SA 035 & Broad Spectrum Antiviral Platform [Member]
Unobservable Input Reconciliation [Roll Forward]
Change in fair value of contingent obligations		100	$ (9,900)	(300)	$ (9,500)
Contingent value rights based on the novation of the contract							$ 4,000
RSDL [Member]
Unobservable Input Reconciliation [Roll Forward]
Change in fair value of contingent obligations		(2,300)	$ (1,900)	(1,000)	$ (1,800)
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Investment in money market funds (1)	[1]	10		10		$ 3,323
Total assets		10		10		3,323
Liabilities [Abstract]
Contingent consideration		22,928		22,928		25,155
Total liabilities		22,928		22,928		25,155
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Investment in money market funds (1)	[1]	10		10		3,323
Total assets		10		10		3,323
Liabilities [Abstract]
Contingent consideration		0		0		0
Total liabilities		0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Investment in money market funds (1)	[1]	0		0		0
Total assets		0		0		0
Liabilities [Abstract]
Contingent consideration		0		0		0
Total liabilities		0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Investment in money market funds (1)	[1]	0		0		0
Total assets		0		0		0
Liabilities [Abstract]
Contingent consideration		22,928		22,928		25,155
Total liabilities		$ 22,928		$ 22,928		$ 25,155

[1] Included in cash and cash equivalents in accompanying consolidated balance sheets