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Employee Benefit Plans - Narrative (Details) - USD ($) | 12 Months Ended
--- | ---
May 31, 2018 | May 31, 2017 | May 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |  |
Accrued benefit liability | $ 27,600,000 | $ 28,000,000 |
Unrecognized net actuarial loss | $ 800,000 | $ 1,200,000 |
Expected return on plan assets (as a percent) | 4.90% | 5.40% |
Expected contributions next twelve months | $ 4,300,000 |  |
Expected contributions in year two | 3,200,000 |  |
Expected contributions in year three | 3,400,000 |  |
Expected contributions in year four | 3,600,000 |  |
Expected contributions in year five | 3,700,000 |  |
Expected contributions in year six | 3,900,000 |  |
Expected contributions thereafter | 21,400,000 |  |
Fair value of plan assets | 58,781,000 | $ 59,396,000 | $ 0
Projected benefit obligation | 86,341,000 | 87,387,000 | 0
Estimated contribution to pension plan | 0 |  |
Net periodic benefit expense (income) | (14,000) | (28,000) |
Supplemental Executive Retirement Plan (SERP) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 8,200,000 | 6,900,000 | 6,600,000
United States Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Required years of service for plan eligibility (years) | 1 year |  |
Employer contributions | $ 56,700,000 | 47,500,000 | 43,100,000
Deferred Profit Sharing Plan (DPSP) |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employer contributions | 2,800,000 | 1,800,000 | $ 1,600,000
Pension Plan of Immaterial Acquisitions |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair value of plan assets | 7,500,000 | 7,100,000 |
Projected benefit obligation | 7,400,000 | 7,500,000 |
Net periodic benefit expense (income) | $ (100,000) | $ 100,000 |

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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + 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 (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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