Incentive Plans - Summary of LFI and Other Similar Deferred Compensation Arrangements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Prepaid Compensation Asset	$ 101,631	$ 74,597
Compensation Liability	314,485	236,273
LFI and Other Similar Deferred Compensation Arrangements [Member]
Deferred Compensation Arrangement With Individual Excluding Share Based Payments And Postretirement Benefits [Line Items]
Prepaid Compensation Asset	101,631	74,597
Prepaid Compensation Asset, Granted	143,289
Prepaid Compensation Asset, Forfeited	(3,134)
Prepaid Compensation Asset, Amortization	(113,119)
Prepaid Compensation Asset, Other	(2)
Compensation Liability	311,400	$ 226,026
Compensation Liability, Granted	143,289
Compensation Liability, Settled	(104,774)
Compensation Liability, Forfeited	(6,979)
Compensation Liability, Increase (decrease) in fair value of underlying investments	40,634
Compensation Liability, Adjustment for estimated forfeitures	10,167
Compensation Liability, Other	$ 3,037