Aggregate notional amount of foreign currency exchange rate derivatives. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Name:	us-gaap_NotionalAmountOfForeignCurrencyDerivatives
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair Value of Financial Instruments - Additional Information (Detail) In Millions, unless otherwise specified	Jun. 30, 2013 USD ($)	Jun. 30, 2013 EUR (€)	Jun. 30, 2013 GBP (£)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 GBP (£)
Fair Value Disclosures [Abstract]
Transfers of financial instruments between levels	$ 0			$ 0
Notional value of foreign currency forward		€ 10.3	£ 75.0		£ 75.0