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Debt - Summary of Debt and Capital Lease Obligations (Parenthetical) (Detail) (USD $)
Apr. 18, 2013
Dec. 31, 2012
Aug. 01, 2011
Jul. 25, 2011
Dec. 31, 2013
$1 Billion Credit Facility [Member]
Dec. 31, 2012
$925 Million Credit Facility [Member]
Dec. 31, 2013
3.75% Convertible Senior Notes [Member]
Dec. 31, 2012
3.75% Convertible Senior Notes [Member]
Dec. 31, 2013
5% Senior Notes [Member]
Dec. 31, 2013
6.75% Senior Notes [Member]
Debt Instrument [Line Items]                    
Total credit facility $ 925,000,000 $ 925,000,000 $ 1,000,000,000 $ 1,000,000,000 $ 1,000,000,000 $ 925,000,000        
Interest rate of Senior Notes             3.75%   5.00% 6.75%
Debt discount on Convertible Senior Notes             $ 10,096,000 $ 26,961,000