Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 States	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Line Items]
Income tax receivable	$ 15.0	$ 5.7
Uncertain tax benefits accrued	4.0	3.9	0.4
Interest and penalties recognized related to uncertain income tax positions	0.1	0.1
Interest and penalties accrued related to uncertain income tax positions	0.1	0.1
Number of individual states subject to income taxes	50
Uncertain tax benefits accrued, ending balance	4.0	3.9	0.4
Other Long Term Obligations [Member]
Income Tax Disclosure [Line Items]
Uncertain tax benefits accrued	0.5
Uncertain tax benefits accrued, ending balance	0.5
Deferred Income Taxes [Member]
Income Tax Disclosure [Line Items]
Uncertain tax benefits accrued	3.5
Uncertain tax benefits accrued, ending balance	3.5
Minimum [Member]
Income Tax Disclosure [Line Items]
Tax years open to examination	2001
Maximum [Member]
Income Tax Disclosure [Line Items]
Tax years open to examination	2014
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	299.0
Tax credits	2.9
Net operating loss carryforwards valuation allowance	0.1	0.2
Tax credit carryforwards valuation allowance	0.4
Net change in total valuation allowance	0.3
Federal [Member]
Income Tax Disclosure [Line Items]
Income tax receivable	14.3
Net operating loss carryforwards	139.0
Tax credits	1.0
Puerto Rico [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 0.7