Marketable Investment Securities (Tables)

12 Months Ended

Jun. 30, 2017

Investments Debt And Equity Securities [Abstract]

Schedule of Fair Value for Available-for-Sale Securities by Major Security Type and Class of Security

The amortized cost, gross unrealized holding gains, gross unrealized holding losses, and fair value for available-for-sale securities by major security type and class of security at June 30, 2017 and 2016 were as follows:

			Gross		Gross
			unrealized		unrealized
	Amortized		holding		holding			Estimated
	cost		gains		losses			fair value
At June 30, 2017:
Cash and cash equivalents:
Cash	$	83.5	$	—	$	—		$	83.5
Cash equivalents		18.9		—		—			18.9
Total cash and cash equivalents		102.4		—		—			102.4
Available-for-sale:
Corporate bonds and notes		45.4		0.1		(0.1	)		45.4
Municipal bonds		32.7		—		—			32.7
Federal agency issues		11.6		—		(0.1	)		11.5
US government securities		7.2		—		—			7.2
Total	$	199.3	$	0.1	$	(0.2	)	$	199.2

			Gross		Gross
			unrealized		unrealized
	Amortized		holding		holding		Estimated
	cost		gains		losses		fair value
At June 30, 2016:
Cash and cash equivalents:
Cash	$	66.1	$	—	$	—	$	66.1
Cash equivalents		2.4		—		—		2.4
Total cash and cash equivalents		68.5		—		—		68.5
Available-for-sale:
Corporate bonds and notes		50.8		0.2		—		51.0
Municipal bonds		85.4		0.2		—		85.6
Federal agency issues		25.5		—		—		25.5
US government securities		8.2		0.1		—		8.3
Total	$	238.4	$	0.5	$	—	$	238.9

Schedule of Maturities of Debt Securities Classified as Cash Equivalents and Available-For-Sale

Cash, cash equivalents, and maturities of debt securities classified as available-for-sale are as follows at June 30, 2017:

	Amortized		Estimated
	cost		fair value
Cash	$	83.5	$	83.5
Cash equivalents		18.9		18.9
Available-for-sale:
Due within one year		48.3		48.3
Due after one year through five years		48.6		48.5
Due after five years		—		—
Total	$	199.3	$	199.2

Schedule of Debt Securities Available-For-Sale in Gross Unrealized Loss Position

Debt securities available-for-sale in a gross unrealized loss position as of June 30, 2017 and 2016 are summarized as follows:

	Less than 12 months				More than 12 months				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	value		losses		value		losses		value		losses
At June 30, 2017:
Debt securities:
Corporate bonds and notes		29.9		0.1		—		—		29.9		0.1
Municipal bonds		13.3		—		0.7		—		14.0		—
Federal agency issues		11.5		0.1		—		—		11.5		0.1
US government securities		5.3		—		—		—		5.3		—
	$	60.0	$	0.2	$	0.7	$	—	$	60.7	$	0.2

	Less than 12 months				More than 12 months				Total
	Fair		Unrealized		Fair		Unrealized		Fair		Unrealized
	value		losses		value		losses		value		losses
At June 30, 2016:
Debt securities:
Corporate bonds and notes		5.0		—		1.5		—		6.5		—
Municipal bonds		7.6		—		6.3		—		13.9		—
Federal agency issues		6.0		—		—		—		6.0		—
US government securities		—		—		—		—		—		—
	$	18.6	$	—	$	7.8	$	—	$	26.4	$	—