Pensions and Postretirement Benefits Other than Pensions - Defined Benefit Pension and Other Postretirement Benefits Plans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amounts recognized in the balance sheets:
Postretirement benefits other than pensions	$ (221,395)	$ (227,216)
Pension Plan
Change in benefit obligation:
Projected Benefit Obligation at beginning of year	1,553,563	1,409,380
Service cost - employer	9,946	8,906
Interest cost	41,560	50,560
Actuarial (gain)/loss	156,946	162,549
Benefits paid	(81,083)	(77,718)
Plan Amendment	2,800	3,069
Settlements	(16,653)	(18,196)
Foreign currency translation effect	11,941	15,013
Projected Benefit Obligation at end of year	1,679,020	1,553,563	$ 1,409,380
Change in plans’ assets:
Fair value of plans’ assets at beginning of year	1,426,556	1,261,130
Actual return on plans’ assets	170,063	198,088
Employer contribution	15,552	48,899
Benefits paid	(81,083)	(77,718)
Settlements	(16,653)	(18,196)
Foreign currency translation effect	12,475	14,353
Fair value of plans’ assets at end of year	1,526,910	1,426,556	1,261,130
Funded status	(152,110)	(127,007)
Amounts recognized in the balance sheets:
Accrued liabilities	0	(300)
Postretirement benefits other than pensions	(152,110)	(126,707)
Other Postretirement Benefits
Change in benefit obligation:
Projected Benefit Obligation at beginning of year	241,550	251,798
Service cost - employer	1,439	1,573	1,948
Interest cost	7,320	9,887	9,251
Actuarial (gain)/loss	(8,277)	(9,664)
Benefits paid	(8,371)	(12,044)
Plan Amendment	0	0
Settlements	0	0
Foreign currency translation effect	0	0
Projected Benefit Obligation at end of year	233,661	241,550	251,798
Change in plans’ assets:
Fair value of plans’ assets at beginning of year	0	0
Actual return on plans’ assets	0	0
Employer contribution	0	0
Benefits paid	0	0
Settlements	0	0
Foreign currency translation effect	0	0
Fair value of plans’ assets at end of year	0	0	0
Funded status	(233,661)	(241,550)
Amounts recognized in the balance sheets:
Accrued liabilities	(12,266)	(14,334)
Postretirement benefits other than pensions	(221,395)	(227,216)
United States
Change in plans’ assets:
Fair value of plans’ assets at beginning of year	1,047,214
Fair value of plans’ assets at end of year	1,117,650	1,047,214
United States | Pension Plan
Change in benefit obligation:
Projected Benefit Obligation at beginning of year	1,106,877	1,004,751
Service cost - employer	9,946	8,906	10,363
Interest cost	33,143	39,499	36,840
Actuarial (gain)/loss	102,678	113,828
Benefits paid	(66,339)	(63,176)
Plan Amendment	2,581	3,069
Settlements	0	0
Foreign currency translation effect	0	0
Projected Benefit Obligation at end of year	1,188,886	1,106,877	1,004,751
Change in plans’ assets:
Fair value of plans’ assets at beginning of year	1,047,214	912,129
Actual return on plans’ assets	132,137	159,949
Employer contribution	4,638	38,312
Benefits paid	(66,339)	(63,176)
Settlements	0	0
Foreign currency translation effect	0	0
Fair value of plans’ assets at end of year	1,117,650	1,047,214	912,129
Funded status	(71,236)	(59,663)
Amounts recognized in the balance sheets:
Accrued liabilities	0	(300)
Postretirement benefits other than pensions	(71,236)	(59,363)
International | Pension Plan
Change in benefit obligation:
Projected Benefit Obligation at beginning of year	446,686	404,629
Service cost - employer	0	0
Interest cost	8,417	11,061	11,161
Actuarial (gain)/loss	54,268	48,721
Benefits paid	(14,744)	(14,542)
Plan Amendment	219	0
Settlements	(16,653)	(18,196)
Foreign currency translation effect	11,941	15,013
Projected Benefit Obligation at end of year	490,134	446,686	404,629
Change in plans’ assets:
Fair value of plans’ assets at beginning of year	379,342	349,001
Actual return on plans’ assets	37,926	38,139
Employer contribution	10,914	10,587
Benefits paid	(14,744)	(14,542)
Settlements	(16,653)	(18,196)
Foreign currency translation effect	12,475	14,353
Fair value of plans’ assets at end of year	409,260	379,342	$ 349,001
Funded status	(80,874)	(67,344)
Amounts recognized in the balance sheets:
Accrued liabilities	0	0
Postretirement benefits other than pensions	$ (80,874)	$ (67,344)