Retirement plans - Reconciliation of Benefit Obligations, Plan Assets and Funded Status of Company-Sponsored Retirement Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 28, 2014
Change in benefit obligations
Benefit obligations at end of year	$ 606,413
Change in plan assets
Fair value of plan assets at end of year	388,168
Funded status at end of year	(218,245)
Amounts recognized in Consolidated Balance Sheets
Accrued benefit cost—noncurrent	(187,290)	$ (178,844)
Retirement Plans
Change in benefit obligations
Benefit obligations at beginning of year	586,624	566,224
Service cost	816	920	$ 812
Interest cost	26,111	23,800	23,558
Actuarial loss (gain)	17,755	(12,514)
Gross benefits paid	(38,532)	(34,401)
Adjustment due to spin-off of publishing businesses	13,639	42,595
Benefit obligations at end of year	606,413	586,624	566,224
Change in plan assets
Fair value of plan assets at beginning of year	400,193	387,626
Actual return on plan assets	21,316	(725)
Employer contributions	5,191	12,008
Gross benefits paid	(38,532)	(34,401)
Transfers	0	35,685
Fair value of plan assets at end of year	388,168	400,193	$ 387,626
Funded status at end of year	(218,245)	(186,431)
Amounts recognized in Consolidated Balance Sheets
Accrued benefit cost—current	(30,955)	(7,587)
Accrued benefit cost—noncurrent	$ (187,290)	$ (178,844)