Business operations and segment information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating revenues		$ 1,903,026	$ 2,004,088	$ 1,764,822
Operating income		545,902	708,152	630,294
Net gain on sale of corporate building	$ 89,900
Depreciation, amortization, asset impairment and facility consolidation charges (gains)		81,067	110,762	27,243
Capital expenditures		39,445	43,215	59,981
Operating Segments | Media
Segment Reporting Information [Line Items]
Operating revenues		1,903,026	1,994,120	1,713,982
Operating income		602,514	800,791	701,995
Depreciation, amortization, asset impairment and facility consolidation charges (gains)		79,398	85,890	83,004
Capital expenditures		39,055	41,572	53,928
Operating Segments | Digital
Segment Reporting Information [Line Items]
Operating revenues		0	9,968	50,840
Operating income		0	(30,241)	(41,059)
Depreciation, amortization, asset impairment and facility consolidation charges (gains)		0	21,166	26,581
Capital expenditures		0	0	5,263
Corporate
Segment Reporting Information [Line Items]
Operating income		(56,612)	(62,398)	(68,595)
Depreciation, amortization, asset impairment and facility consolidation charges (gains)		1,669	3,706	(82,342)
Capital expenditures		390	1,643	790
Segment Reconciling Items
Segment Reporting Information [Line Items]
Net gain on sale of corporate building		0	0	89,892
Unallocated
Segment Reporting Information [Line Items]
Operating income		$ 0	$ 0	$ (51,939)