Significant agreements - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Contract assets
Balance at the beginning of year	$ 0	$ 0
Additions		149
Deductions		(149)
Impact of exchange rates		0
Balance at the end of year		0
Contract liabilities:
Balance at the beginning of year	5,657	14,635
Additions	31,000	1,172
Deductions	(1,129)	(10,413)
Impact of exchange rates	(1,275)	263
Balance at the end of year	34,253	5,657
AstraZeneca
Contract liabilities:
Balance at the beginning of year	4,913	4,727
Additions		58
Deductions	(412)	(35)
Impact of exchange rates	157	163
Balance at the end of year	4,658	4,913
Sanofi
Contract liabilities:
Balance at the beginning of year	0	9,908
Additions		0
Deductions		(9,984)
Impact of exchange rates		76
Balance at the end of year	0	0
Dementia Discovery Fund
Contract assets
Balance at the beginning of year	744	0
Additions		1,114
Deductions		(394)
Impact of exchange rates		24
Balance at the end of year		744
Contract liabilities:
Balance at the beginning of year	744
Deductions	(56)
Impact of exchange rates	(48)
Balance at the end of year	640	$ 744
Genetech
Contract liabilities:
Additions	31,000
Deductions	(661)
Impact of exchange rates	(1,384)
Balance at the end of year	$ 28,955