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Marketable Investment Securities - Schedule of Fair Value for Available-for-Sale Securities by Major Security Type and Class of Security (Detail) - USD ($) $ in Millions | Sep. 30, 2016 | Jun. 30, 2016 | Sep. 30, 2015 | Jun. 30, 2015
--- | --- | --- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | $ 86.9 | $ 68.5 | $ 87.4 | $ 64.1
Amortized cost | 200.4 | 238.4 |  |
Gross unrealized holding gains | 0.2 | 0.5 |  |
Gross unrealized holding losses | 0.0 | 0.0 |  |
Estimated fair value | 200.6 | 238.9 |  |
Amortized cost | 200.4 | 238.4 |  |
Estimated fair value | 200.6 | 238.9 |  |
Corporate Bonds and Notes |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 45.4 | 50.8 |  |
Gross unrealized holding gains | 0.1 | 0.2 |  |
Gross unrealized holding losses | 0.0 | 0.0 |  |
Estimated fair value | 45.5 | 51.0 |  |
Municipal Bonds |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 52.2 | 85.4 |  |
Gross unrealized holding gains | 0.1 | 0.2 |  |
Gross unrealized holding losses | 0.0 | 0.0 |  |
Estimated fair value | 52.3 | 85.6 |  |
Federal Agency Issues |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 12.6 | 25.5 |  |
Gross unrealized holding losses | 0.0 | 0.0 |  |
Estimated fair value | 12.6 | 25.5 |  |
Cash |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 61.1 | 66.1 |  |
Estimated fair value | 61.1 | 66.1 |  |
Cash Equivalents |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 25.8 | 2.4 |  |
Estimated fair value | 25.8 | 2.4 |  |
Total Cash and Cash Equivalents |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 86.9 | 68.5 |  |
Estimated fair value | 86.9 | 68.5 |  |
US Government Securities |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 3.3 | 8.2 |  |
Gross unrealized holding gains |  | 0.1 |  |
Gross unrealized holding losses | 0.0 | 0.0 |  |
Estimated fair value | $ 3.3 | $ 8.3 |  |

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563 + Details
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