Pension Plans and Other Postretirement Benefits - Changes in Level 3 Pension Plan Assets Measured at Fair Value on Recurring Basis (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	$ 2,418,702
Fair value of plan assets at end of year	2,593,533
Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	283,754
Fair value of plan assets at end of year	349,039
Other Real Estate Partnerships [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	23,231
Purchase(Sales)	(31,299)
Total Realized/Unrealized Gains (Losses)	19,424
Fair value of plan assets at end of year	11,356
Other Private Equity [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	97,124
Purchase(Sales)	27,170
Total Realized/Unrealized Gains (Losses)	27,256
Fair value of plan assets at end of year	151,550
Other Hedge Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	152,901
Purchase(Sales)	(2,322)
Total Realized/Unrealized Gains (Losses)	25,513
Fair value of plan assets at end of year	176,092
Guaranteed Deposit Fund [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	10,498
Fair value of plan assets at end of year	10,041
Guaranteed Deposit Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	10,498
Total Realized/Unrealized Gains (Losses)	(457)
Fair value of plan assets at end of year	10,041
Other Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	479,393
Fair value of plan assets at end of year	537,141
Other Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	283,754
Purchase(Sales)	(6,451)
Total Realized/Unrealized Gains (Losses)	71,736
Fair value of plan assets at end of year	$ 349,039