Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Foreign currency translation	$ (266,247)	$ (403,941)
Unrealized loss on net investment hedge, net of tax	(17,388)	0
Unrecognized net actuarial loss, net of tax	(566,876)	(611,333)
Unrecognized prior service (cost) credit, net of tax	(2,081)	2,253
Total accumulated other comprehensive loss	$ (852,592)	$ (1,013,021)