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Treasury Stock - Schedule of repurchase of common stock (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 43 Months Ended |  |
--- | --- | --- | --- | --- | ---
Feb. 28, 2019 | Nov. 30, 2018 | Aug. 31, 2018 | Feb. 28, 2018 | Nov. 30, 2017 | Aug. 31, 2017 | Feb. 28, 2019 | Feb. 28, 2019 | Mar. 21, 2018 | Jul. 22, 2015
Stockholders' Equity Attributable to Parent [Abstract] |  |  |  |  |  |  |  |  |  |
Authorized amount of stock to be repurchased | $ 100.0 |  |  |  |  |  | $ 100.0 | $ 100.0 | $ 50.0 | $ 50.0
Total current Board authorizations | (2.0) | $ 0.0 | $ 0.0 | $ (11.9) | $ (8.6) | $ (4.7) | 0.0 | (40.6) |  |
Less repurchases made under these authorizations | $ 59.4 |  |  |  |  |  | $ 59.4 | $ 59.4 |  |

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- Definition Amount of stock repurchase plan authorized. + References No definition available. + Details
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- Definition Amount remaining of a stock repurchase plan authorized. + References No definition available. + Details
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- Definition Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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