Financial Guarantees - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financial Guarantees [Line Items]
Term of standby letters of credit, years	1 year
Notional amount of standby letters of credit	$ 71.5	$ 63.4
Carrying value of letters of credit	0.3	0.4
Interest rate swap, notional amount	141.0	41.0
Interest rate swap [Member]
Financial Guarantees [Line Items]
Interest rate swap, notional amount	$ 8.3