Significant agreements - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Contract assets
Balance at the beginning of year	$ 0	$ 0
Additions	103	91
Deductions	0	(91)
Impact of exchange rates	0	0
Balance at the end of year	103	0
Change in Contract with Customer, Liability [Abstract]
Balance at the beginning of year	14,635	14,467
Additions	1,138	5,350
Deductions	(5,424)	(4,472)
Impact of exchange rates	21	(710)
Balance at the end of year	10,370	14,635
Sanofi
Change in Contract with Customer, Liability [Abstract]
Balance at the beginning of year	9,908	14,467
Additions	0	0
Deductions	(5,286)	(4,006)
Impact of exchange rates	34	(553)
Balance at the end of year	4,656	9,908
AstraZeneca
Change in Contract with Customer, Liability [Abstract]
Balance at the beginning of year	4,727	0
Additions	24	5,350
Deductions	(35)	(466)
Impact of exchange rates	(14)	(157)
Balance at the end of year	4,702	4,727
Dementia Discovery Fund
Change in Contract with Customer, Liability [Abstract]
Balance at the beginning of year	0
Additions	1,114
Deductions	(103)
Impact of exchange rates	1
Balance at the end of year	$ 1,012	$ 0