Income taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Provisional income tax (expense) benefit due to tax cuts and jobs act	$ 46,100
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)	$ 154,000
Tax cuts and jobs act of 2017, incomplete accounting, expected period to pay provisional income tax expense (benefit)	8 years
Cumulative unremitted earnings, non-permanently reinvested	$ 2,000,000
Effective income tax rate, total	45.50%	3.30%	3.20%
Deferred tax asset, income tax expense (benefit) due to tax cuts and jobs act of 2017	$ 107,900
Tax cuts and jobs act of 2017, transition tax for accumulated foreign earnings, liability	154,000
Realized net benefit as result of reducing our reserves with respect to uncertain tax positions	5,200	$ 8,800	$ 4,600
Tax effect, carry forwards	$ 210,100
Percentage of change in ownership	50.00%
Deferred tax assets, valuation allowance	$ 104,799	104,520
Unrecognized tax benefits that would impact effective tax rate	5,000
Unrecognized tax benefits, interest (benefit) expense	200	200	1,600
Unrecognized tax benefits, penalties	(200)	(500)	$ (400)
Unrecognized tax benefits, interest (benefit) expense accrued	600	700
Unrecognized tax benefits, penalties accrued	2,600	$ 2,700
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	1,600
No Expiration Date
Income Tax Contingency [Line Items]
Tax effect, carry forwards	11,500
After 2013 but before the end of 2018
Income Tax Contingency [Line Items]
Tax effect, carry forwards	2,000
After 2018
Income Tax Contingency [Line Items]
Tax effect, carry forwards	$ 196,600
Excess Tax Deductions
Income Tax Contingency [Line Items]
Effective income tax rate, total	45.50%	3.30%