Calculation of Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) (8.25% Convertible debentures [Member])	3 Months Ended
Mar. 31, 2013
8.25% Convertible debentures [Member]
Calculation Of Numerator And Denominator In Earnings Per Share [Line Items]
Interest rate, Convertible debentures	8.25%

The effective interest rate on the liability component of convertible debt instrument which may be settled in cash upon conversion, including partial cash settlement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 20

-Section 50

-Paragraph 6

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6036836-161870

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number APB14-1

-Paragraph 33

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_DebtInstrumentConvertibleEffectiveInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration