Goodwill and other intangible assets - Summary of the Change in Net Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 28, 2014
Goodwill [Roll Forward]
Goodwill before accumulated impairment losses beginning balance		$ 4,094,697	$ 4,081,742
Accumulated impairment losses beginning balance		(174,971)	(166,971)
Beginning Balance		3,919,726	3,914,771
Acquisitions & adjustments		176,775	26,484
Dispositions			(252)
Impairment		(15,218)	(8,000)	$ (30,300)
Foreign currency exchange rate changes		(13,754)	(13,277)
Goodwill before accumulated impairment losses beginning balance		4,257,718	4,094,697	4,081,742
Accumulated impairment losses ending balance		(190,189)	(174,971)	(166,971)
Ending Balance		4,067,529	3,919,726	3,914,771
Media
Goodwill [Roll Forward]
Goodwill before accumulated impairment losses beginning balance		2,579,418	2,578,601
Accumulated impairment losses beginning balance		0	0
Beginning Balance		2,579,418	2,578,601
Acquisitions & adjustments		0	817
Dispositions			0
Impairment		0	0
Foreign currency exchange rate changes		0	0
Goodwill before accumulated impairment losses beginning balance		2,579,418	2,579,418	2,578,601
Accumulated impairment losses ending balance		0	0	0
Ending Balance		2,579,418	2,579,418	2,578,601
Digital
Goodwill [Roll Forward]
Goodwill before accumulated impairment losses beginning balance		1,515,279	1,503,141
Accumulated impairment losses beginning balance		(174,971)	(166,971)
Beginning Balance		1,340,308	1,336,170
Acquisitions & adjustments		176,775	25,667
Dispositions			(252)
Impairment	$ (15,200)	(15,218)	(8,000)
Foreign currency exchange rate changes		(13,754)	(13,277)
Goodwill before accumulated impairment losses beginning balance		1,678,300	1,515,279	1,503,141
Accumulated impairment losses ending balance		(190,189)	(174,971)	(166,971)
Ending Balance		$ 1,488,111	$ 1,340,308	$ 1,336,170