Shareholders' equity - change in accumulated other comprehensive income (loss), net of tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss), net of tax	$ (260,895)	$ (110,855)
Other comprehensive income (loss) before reclassifications	(114,845)	(152,275)
Amounts reclassified from accumulated other comprehensive income (loss)	4,616	2,235
Net current-year other comprehensive income (loss)	(110,229)	(150,040)
Ending balance, accumulated other comprehensive income (loss), net of tax	(371,124)	(260,895)
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss), net of tax	0	0
Other comprehensive income (loss) before reclassifications	(2,974)	594
Amounts reclassified from accumulated other comprehensive income (loss)	483	(594)
Net current-year other comprehensive income (loss)	(2,491)	0
Ending balance, accumulated other comprehensive income (loss), net of tax	(2,491)	0
Pension and Other Postretirement Benefits Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss), net of tax	(141,744)	(97,037)
Other comprehensive income (loss) before reclassifications	(1,276)	(47,536)
Amounts reclassified from accumulated other comprehensive income (loss)	4,133	2,829
Net current-year other comprehensive income (loss)	2,857	(44,707)
Ending balance, accumulated other comprehensive income (loss), net of tax	(138,887)	(141,744)
Foreign Currency Translation Adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, accumulated other comprehensive income (loss), net of tax	(119,151)	(13,818)
Other comprehensive income (loss) before reclassifications	(110,595)	(105,333)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Net current-year other comprehensive income (loss)	(110,595)	(105,333)
Ending balance, accumulated other comprehensive income (loss), net of tax	$ (229,746)	$ (119,151)