Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2017

Fair Value Disclosures [Abstract]

Carrying amount and estimated fair value, long-term debt

The carrying amounts and estimated fair values of the Company's long-term debt at June 30, 2017 and December 31, 2016 were as follows:

	June 30, 2017				December 31, 2016				Fair Value Level Hierarchy
	Carrying Value		Estimated Fair Value		Carrying Value		Estimated Fair Value
	(in millions)
Senior term loans	$	435.0	$	453.8	$	451.9	$	463.9	Level 3
Junior term loans	43.2		44.7		47.1		48.1		Level 3
Fixed-rate loans	216.3		221.5		—		—		Level 3
Class A enhanced equipment trust certificates	423.6		436.3		409.8		416.0		Level 2
Class B enhanced equipment trust certificates	100.0		102.3		103.6		105.7		Level 2
Total long-term debt	$	1,218.1	$	1,258.6	$	1,012.4	$	1,033.7

Schedule of assets and liabilities measured at fair value on a recurring basis

Assets and liabilities measured at gross fair value on a recurring basis are summarized below:

	Fair Value Measurements as of June 30, 2017
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	869.2	$	869.2	$	—	$	—
Short-term investment securities	100.5		100.5		—		—
Total assets	$	969.7	$	969.7	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

	Fair Value Measurements as of December 31, 2016
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	700.9	$	700.9	$	—	$	—
Short-term investment securities	100.2		100.2		—		—
Total assets	$	801.1	$	801.1	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—