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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	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 120.5	$ 64.1	$ 55.2	$ 64.8
Gross unrealized holding gains	0.4	0.1
Gross unrealized holding losses	(0.1)	(0.1)
Amortized cost	286.1	185.4
Estimated fair value	286.4	185.4
Corporate Bonds and Notes
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	48.5	41.8
Gross unrealized holding gains	0.1
Gross unrealized holding losses	(0.1)
Estimated fair value	48.5	41.8
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	80.6	66.3
Gross unrealized holding gains	0.2	0.1
Gross unrealized holding losses		(0.1)
Estimated fair value	80.8	66.3
Federal Agency Issues
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	36.5	13.2
Gross unrealized holding gains	0.1
Estimated fair value	36.6	13.2
Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	114.2	54.7
Estimated fair value	114.2	54.7
Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	6.3	9.4
Estimated fair value	6.3	9.4
Total Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	120.5	64.1
Estimated fair value	$ 120.5	$ 64.1

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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