Income Taxes (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Income Tax Examination [Line Items]
Unrecognized tax benefit	$ 0.4
Reduction in income tax expense resulting from recognition of unrecognized tax benefit	$ 0.3
Federal tax
Income Tax Examination [Line Items]
Tax years open to examination	Our U.S. federal tax returns for 2008, 2010 and subsequent years remain open to examination
State tax
Income Tax Examination [Line Items]
Tax years open to examination	Our California tax returns for 2008 and subsequent tax years remain open to examination. Massachusetts tax returns for 2008, 2010 and subsequent years remain open to examination