Income taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Cumulative unremitted earnings, non-permanently reinvested	$ 545,500,000
Cumulative unremitted earnings	966,200,000
Effective income tax rate, total	13.02%	13.40%	(9.93%)
Realized net benefit as result of reducing our reserves with respect to uncertain tax positions	1,800,000	7,100,000	8,000,000
Tax effect, carry forwards	112,800,000
Percentage of change in ownership	50.00%
Deferred tax assets, valuation allowance	99,141,000	86,510,000
Unrecognized tax benefits that would impact effective tax rate	21,600,000
Unrecognized tax benefits, interest (benefit) expense	1,000,000	1,300,000	800,000
Unrecognized tax benefits, penalties	(800,000)	(800,000)	200,000
Unrecognized tax benefits, interest (benefit) expense accrued	6,200,000	5,700,000
Unrecognized tax benefits, penalties accrued	5,000,000	6,000,000
Unrecognized tax benefits change within next twelve months due to potential for resolution of foreign and U.S. examinations	(2,230,000)	258,000	169,000
Minimum
Income Tax Contingency [Line Items]
Unrecognized tax benefits change within next twelve months due to potential for resolution of foreign and U.S. examinations	0
Maximum
Income Tax Contingency [Line Items]
Unrecognized tax benefits change within next twelve months due to potential for resolution of foreign and U.S. examinations	2,600,000
No Expiration Date
Income Tax Contingency [Line Items]
Tax effect, carry forwards	12,600,000
After 2013 but before the end of 2018
Income Tax Contingency [Line Items]
Tax effect, carry forwards	300,000
After 2018
Income Tax Contingency [Line Items]
Tax effect, carry forwards	$ 99,900,000
Excess Tax Deductions
Income Tax Contingency [Line Items]
Effective income tax rate, total	13.00%	13.40%