Retirement plans - Reconciliation of Benefit Obligations, Plan Assets and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 30, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 30, 2018
Change in plan assets
Fair value of plan assets at beginning of year	$ 54,035
Fair value of plan assets at end of year	2,859,436	$ 54,035
Reconciliation of funded status:
Fair value of assets at end of period	54,035	54,035		$ 2,859,436	$ 54,035
Retirement Plans
Change in benefit obligations
Benefit obligations at beginning of year	74,190	82,344
Service cost	999	606	$ 630
Interest cost	12,408	2,775	3,143
Actuarial gain	3,701	(6,228)
Foreign currency translation	11,812	0
Benefits and expenses paid	(111,842)	(5,307)
Acquisitions	2,981,914	0
Benefit obligations at end of year	2,973,182	74,190	82,344
Change in plan assets
Fair value of plan assets at beginning of year	54,035	61,539
Actual return on plan assets	38,054	(3,648)
Employer contributions	91,466	1,451
Acquisitions	2,771,796	0
Gross benefits paid	(111,022)	(4,705)
Foreign currency translation	12,787	0
Expenses paid	(820)	(602)
Fair value of plan assets at end of year	2,856,296	54,035	61,539
Reconciliation of funded status:
Benefit obligation at end of period	(2,973,182)	(74,190)	(82,344)	(2,973,182)	(74,190)
Fair value of assets at end of period	$ 2,856,296	$ 54,035	$ 61,539	2,856,296	54,035
Funded status				(116,886)	(20,155)
Unrecognized actuarial (gain) loss				(4,527)	7,986
Balance sheet presentation:
Other assets				58,818	0
Accrued expenses				6,771	0
Pension and other postretirement benefit obligations				168,933	20,155
Accumulated other comprehensive income				4,527	(7,986)
Net accrued benefit cost				$ (121,413)	$ (12,169)