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Retirement Plans - Reconciliation of Balances of Pension Benefit Obligation and Fair Value of Plan Assets (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Change in pension benefit obligation: |  |  |
Benefit obligation at beginning of year | $ 274,400,000 | $ 253,200,000 |
Service cost | 800,000 | 1,600,000 | $ 800,000
Interest cost | 8,000,000.0 | 9,800,000 | 9,300,000
Net actuarial loss | 22,600,000 | 24,700,000 |
Benefits paid | (15,200,000) | (14,900,000) |
Benefit obligation at end of year | 290,600,000 | 274,400,000 | 253,200,000
Change in plan assets: |  |  |
Fair value of plan assets at beginning of year | 243,700,000 | 220,000,000.0 |
Actual return on plan assets | 34,300,000 | 38,600,000 |
Contributions by the company | 0 | 30,000,000.0 | 0
Benefits paid | (15,200,000) | (14,900,000) |
Fair value of plan assets at end of year | 262,800,000 | 243,700,000 | $ 220,000,000.0
Funded status of the plan (underfunded) | (27,800,000) | (30,700,000) |
Amounts recognized in the consolidated balance sheet consist of: |  |  |
Noncurrent liabilities - accrued benefit liability | (27,800,000) | (30,700,000) |
Accumulated other comprehensive loss - net actuarial loss | 68,300,000 | 69,800,000 |
Net amount included in retained earnings | $ 40,500,000 | $ 39,100,000 |

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- Definition Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 + Details
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