Income taxes - Reconciliation items from U.S. statutory income tax rate to the effective tax rate (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. statutory income tax rate	21.00%	35.00%	35.00%
U.S. tax benefit for foreign derived intangible income	(5.30%)	(0.00%)	(0.00%)
U.S. Tax Act transitional non-cash expense	4.20%	0.00%	0.00%
U.S. Tax Act enactment-date effects and measurement period adjustments	(0.70%)	12.70%	(0.00%)
U.S. tax on global intangible low-taxed income	0.40%	0.00%	0.00%
U.S. tax benefit for manufacturing	(0.00%)	(1.60%)	(1.50%)
U.S. excess tax benefit for stock compensation	(2.00%)	(4.10%)	(3.00%)
U.S. R&D tax credit	(1.30%)	(1.10%)	(1.20%)
U.S. non-deductible expenses	0.20%	0.20%	0.30%
Non-U.S. effective tax rates	0.10%	(2.50%)	(3.70%)
Impact of changes to uncertain tax positions	0.00%	0.70%	0.60%
Other	(0.10%)	0.10%	0.60%
Effective tax rate	16.50%	39.40%	27.10%