Shareholders' equity - Change in accumulated other comprehensive income (loss), net of tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 2,979,320	$ 2,539,978
Other comprehensive income (loss) before reclassifications	39,395	(7,554)
Amounts reclassified from accumulated other comprehensive (loss) income	7,699	4,247
Net current-year other comprehensive (loss) income	47,094	(3,307)
Ending Balance	3,336,457	2,979,320
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	735	807
Other comprehensive income (loss) before reclassifications	(3,331)	1,062
Amounts reclassified from accumulated other comprehensive (loss) income	2,114	(1,134)
Net current-year other comprehensive (loss) income	(1,217)	(72)
Ending Balance	(482)	735
Pension and Other Postretirement Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(138,810)	(131,380)
Other comprehensive income (loss) before reclassifications	(17,032)	(12,811)
Amounts reclassified from accumulated other comprehensive (loss) income	5,585	5,381
Net current-year other comprehensive (loss) income	(11,447)	(7,430)
Ending Balance	(150,257)	(138,810)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(206,317)	(210,512)
Other comprehensive income (loss) before reclassifications	59,758	4,195
Amounts reclassified from accumulated other comprehensive (loss) income	0	0
Net current-year other comprehensive (loss) income	59,758	4,195
Ending Balance	(146,559)	(206,317)
Accumulated Other Comprehensive Income (loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(344,392)	(341,085)
Ending Balance	$ (297,298)	$ (344,392)