Exercisable Options (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011 Year	Dec. 31, 2010 Year	Dec. 31, 2009 Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average remaining contractual life of exercisable options (in years)	5.3	5.3	5.3
Total intrinsic value of exercisable options	$ 128,900	$ 143,900	$ 103,600

The weighted average period between the balance sheet date and expiration for all vested portions of options outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value for number of years.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration