Computation of Earnings Per Share (Parenthetical) (Detail)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
4.5 % Senior Limited Subordination Convertible Notes
Earnings Loss Per Share [Line Items]
Debt instrument convertible effective interest rate	4.50%	4.50%
4.5% Convertible Notes
Earnings Loss Per Share [Line Items]
Debt instrument convertible effective interest rate	4.50%	4.50%
6% Convertible Junior Subordinated Debentures
Earnings Loss Per Share [Line Items]
Debt instrument convertible effective interest rate	6.00%	6.00%
6% Senior Convertible Notes
Earnings Loss Per Share [Line Items]
Debt instrument convertible effective interest rate	6.00%	6.00%

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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