Employee Benefit Plans (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost	$ 16,000,000.0	$ 28,900,000
Net actuarial loss expected to be recognized	$ 6,100,000
Percentage of equity investments in mutual fund	66.00%
Net periodic benefit cost, Expected return on plan assets	7.25%	7.25%	7.25%
Expected defined benefit plans contribution within a year	$ 1,200,000
Number of stock plans	3
Share-based compensation arrangement by share-based payment award, number of shares available for grant	887,189
Dividends, share-based compensation	$ 0.72	$ 0.71	$ 0.67
Weighted-average risk-free interest rate	0.19%	1.65%	2.95%
Performance Shares [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Award payout percentage at less than 25th percentile level of achievement	0.00%
Award payout percentage at the 25th percentile level of achievement	50.00%
Award payout percentage at the 50th percentile level of achievement	100.00%
Award payout percentage at the 75th percentile level of achievement	150.00%
Performance Shares [Member] | Pro Forma [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Granted in period, number of shares/units	48,409	34,317	30,466
Share-based Payment Arrangement, Option [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Options awarded during period	0	0	0
Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	62.00%
Fixed Income Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	36.00%
Two Thousand Fifteen Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Vesting period of options awarded, years	10 years
Cliff vesting period, years	4 years
Two Thousand Fifteen Plan [Member] | Non Vested Stock Awards and Stock Units [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years	10 years
Cliff vesting period, years	4 years
Maximum [Member] | Performance Shares [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Granted in period, number of shares/units	72,618	51,479	45,703
Deferred Profit Sharing [Member] | Qualified Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost		$ 12,600,000	$ 11,900,000
Other Pension Plan [Member] | Qualified Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost		$ 16,300,000	$ 15,000,000.0
Contribution percentage of eligible compensation	2.00%
Maximum annual contributions per employee, percent	50.00%
Participants contribution eligible for match	100.00%
Other Pension Plan [Member] | Qualified Plan [Member] | Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Employer matching contribution, percent of employees' gross pay	6.00%