Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Income Taxes [Line Items]
Unrecognized tax benefit	0.9
Reduction in income tax expense resulting from recognition of unrecognized tax benefit	0.7
Internal Revenue Service (IRS)
Income Taxes [Line Items]
Tax years open to examination	Our U.S. federal tax returns for 2006 and subsequent years remain open to examination.
Tax years under examination	We are currently under audit examination by the IRS for the 2008 and 2009 tax years, which began in July 2011.
State and Local Jurisdiction
Income Taxes [Line Items]
Tax years open to examination	Our California tax returns for 2006 and subsequent years remain open to examination. Our Massachusetts tax returns for 2008 and subsequent years remain open to examination.