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, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 87.4	$ 64.1	$ 69.8	$ 64.8
Gross unrealized holding gains	0.2
Amortized cost	198.3	185.4
Estimated fair value	198.5	185.4
Corporate Bonds and Notes
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	30.6	41.8
Estimated fair value	30.6	41.8
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	57.4	66.3
Gross unrealized holding gains	0.2	0.1
Gross unrealized holding losses		(0.1)
Estimated fair value	57.6	66.3
Federal Agency Issues
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	22.9	13.2
Gross unrealized holding gains		0.1
Gross unrealized holding losses		(0.1)
Estimated fair value	22.9	13.2
Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	67.7	54.7
Estimated fair value	67.7	54.7
Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19.7	9.4
Estimated fair value	19.7	9.4
Total Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	87.4	64.1
Estimated fair value	$ 87.4	$ 64.1