Income taxes - reconciliations between statutory federal income tax rate and effective income tax rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	35.00%	35.00%
Tax effect of international items	(28.41%)	(22.54%)	(14.83%)
State taxes, net of federal benefit	(0.68%)	2.10%	(0.32%)
Uncertain tax contingencies	(1.89%)	(0.83%)	(4.06%)
Contingent consideration reversals	(0.66%)	(1.18%)	(2.04%)
Other, net	(0.16%)	0.47%	(0.35%)
Effective income tax rate, total	3.20%	13.02%	13.40%