Summary of Derivative Financial Instruments by Nature of Underlying Asset or Liability (Detail) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Derivative [Line Items]
Notional Amount	$ 703,286	$ 578,959
Fair Value Hedges
Derivative [Line Items]
Notional Amount	$ 703,286	$ 578,959

Aggregate notional amount of all derivatives. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

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_NotionalAmountOfDerivatives
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant