Investments (Tables)

12 Months Ended

Dec. 31, 2016

Investments

Schedule of marketable investments classified as held-to-maturity

        Marketable investments classified as held-to-maturity consist of the following (in millions):

As of December 31, 2016	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Government-sponsored enterprises	$	19.3	$	—	$	—	$	19.3
Corporate notes and bonds		10.8		—		—		10.8
Total	$	30.1	$	—	$	—	$	30.1
Reported under the following captions on the consolidated balance sheet:
Current marketable investments	$	27.8
Non-current marketable investments		2.3
	$	30.1

As of December 31, 2015	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Government-sponsored enterprises	$	53.3	$	—	$	(0.2	)	$	53.1
Corporate notes and bonds		106.7		—		—			106.7
Total	$	160.0	$	—	$	(0.2	)	$	159.8
Reported under the following captions on the consolidated balance sheet:
Current marketable investments	$	122.0
Non-current marketable investments		38.0
	$	160.0

Summary of gross unrealized losses and the length of time marketable investments have been in a continuous unrealized loss position

        The following table summarizes gross unrealized losses and the length of time marketable investments have been in a continuous unrealized loss position (in millions)

	As of December 31,
	2016				2015
	Fair Value		Gross Unrealized Loss		Fair Value		Gross Unrealized Loss
Government-sponsored enterprises:
Continuous unrealized loss position less than one year	$	—	$	—	$	48.1	$	(0.2	)
Continuous unrealized loss position greater than one year		—		—		—		—
		—		—		48.1		(0.2	)
Corporate notes and bonds:
Continuous unrealized loss position less than one year		—		—		63.8		—
Continuous unrealized loss position greater than one year		—		—		—		—
		—		—		63.8		—
Total	$	—	$	—	$	111.9	$	(0.2	)

Summary of the contractual maturities of held-to-maturity marketable investments

        The following table summarizes the contractual maturities of held-to-maturity marketable investments (in millions):

	As of December 31, 2016
	Amortized Cost		Fair Value
Due in less than one year	$	27.8	$	27.8
Due in one to two years		2.3		2.3
Due in three to five years		—		—
Due after five years		—		—
Total	$	30.1	$	30.1