Income taxes (Reconciliation of Federal Statutory Tax Rate) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
2017 Tax Act, net repatriation tax	71.50%	0.00%	0.00%
Foreign earnings	(15.80%)	(15.50%)	(18.10%)
2017 Tax Act, net deferred tax remeasurement	(7.70%)	0.00%	0.00%
Credits, Puerto Rico Excise Tax	(2.20%)	(2.30%)	(2.50%)
Share-based payments	(0.70%)	(1.30%)	(0.00%)
Credits, primarily federal R&D	(0.60%)	(0.70%)	(1.40%)
State taxes	0.30%	0.10%	0.10%
Audit settlements (federal, state, foreign)	(0.30%)	(0.00%)	(0.50%)
Other, net	(0.10%)	0.40%	0.40%
Effective tax rate	79.40%	15.70%	13.00%