Income taxes - reconciliations between statutory federal income tax rate and effective income tax rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	35.00%	35.00%
Tax effect of international items	(3.30%)	(25.70%)	(27.50%)
Impacts of the TCJA	(1.00%)	37.90%	0.00%
Excess tax benefits related to share-based compensation	(7.20%)	(2.30%)	0.00%
State taxes, net of federal benefit	(0.10%)	0.10%	0.90%
Uncertain tax contingencies	(0.40%)	(1.80%)	(3.60%)
Contingent consideration	5.30%	0.40%	(1.20%)
Intellectual property impairment charge	(2.00%)	0.00%	0.00%
Research and development tax credit	(1.60%)	(0.80%)	(0.60%)
Other, net	(0.10%)	2.70%	0.30%
Effective income tax rate, total	10.60%	45.50%	3.30%