Other assets and investments - Narrative (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 28, 2014
Schedule of Cost-method Investments [Line Items]
Net gains in trading securities	$ 3,200	$ 500	$ 2,900
Pre-tax impairments on equity method investments	3,900	0	3,000
Equity (losses) income in unconsolidated investments, net	(7,170)	(5,064)	151,462
Pre-tax gain on sale of equity method investment			$ 148,400
Other long term assets
Schedule of Cost-method Investments [Line Items]
Cost method investments	$ 21,800	$ 8,600

Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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