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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% |  |

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