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, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligations
Benefit obligations as of end of year	$ 613,695
Change in plan assets
Fair value of plan assets as of end of year	479,735
Funded status as of end of year	(133,960)
Amounts recognized in Consolidated Balance Sheets
Pension liabilities—non-current	(127,146)	$ (139,375)
Retirement Plans
Change in benefit obligations
Benefit obligations as of beginning of year	554,795	614,111
Service cost	8	12	$ 872
Interest cost	23,066	21,337	23,985
Actuarial loss (gain)	73,906	(40,135)
Benefits paid	(34,771)	(36,222)
Acquisition of KFMB	0	25,966
Settlements	(3,309)	(30,274)
Benefit obligations as of end of year	613,695	554,795	614,111
Change in plan assets
Fair value of plan assets as of beginning of year	407,550	439,149
Actual gain (loss) return on plan assets	87,165	(29,016)
Employer contributions	23,100	45,219
Benefits paid	(34,771)	(36,222)
Acquisition of KFMB	0	18,694
Settlements	(3,309)	(30,274)
Fair value of plan assets as of end of year	479,735	407,550	$ 439,149
Funded status as of end of year	(133,960)	(147,245)
Amounts recognized in Consolidated Balance Sheets
Accrued liabilities other—current	(6,814)	(7,870)
Pension liabilities—non-current	$ (127,146)	$ (139,375)