Discontinued operations - Income Statement Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 28, 2014	Dec. 29, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax	$ 102,064	$ 374,235	$ 347,217
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	1,591,031	3,382,033	3,558,239
Income (loss) from discontinued operations, before income taxes	133,152	365,363	447,295
Provision for income taxes	31,088	(8,871)	100,078
Income (loss) from discontinued operations, net of tax	102,064	374,234	347,217
Publishing | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	1,400,006	3,133,861	3,299,793
Income (loss) from discontinued operations, before income taxes	169,220	372,549	441,286
Provision for income taxes	43,735	(11,817)	97,246
Income (loss) from discontinued operations, net of tax	125,485	384,366	344,040
Other | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	191,025	248,172	258,446
Income (loss) from discontinued operations, before income taxes	(36,068)	(7,186)	6,009
Provision for income taxes	(12,647)	2,946	2,832
Income (loss) from discontinued operations, net of tax	$ (23,421)	$ (10,132)	$ 3,177