Debt - 3.75% Convertible Senior Notes - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended			3 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 $1 Billion Credit Facility [Member]	Dec. 31, 2013 $1 Billion Credit Facility [Member]	Mar. 31, 2014 3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Conversion rate per $ 1,000 principal of convertible notes				47.4034
Common Stock principal amount of convertible notes				$ 1,000
Conversion price per share				$ 21.10
Total credit facility		$ 1,000,000,000	$ 1,000,000,000
Strike price of purchased option	21.10
Purchased options number of shares	14.4
Approximate number of common stock share which can be purchased under warrants	14.5
Exercise price of common stock	25.31			25.31