Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Income Taxes [Line Items]
Unrecognized tax benefit	0.5
Reduction in income tax expense resulting from recognition of unrecognized tax benefit	0.3
Internal Revenue Service (IRS)
Income Taxes [Line Items]
Tax years open to examination	Our U.S. federal tax returns for 2010 and subsequent years remain open to examination
State and Local Jurisdiction
Income Taxes [Line Items]
Tax years open to examination	Our California and Massachusetts tax returns for 2008 and subsequent years remain open to examination