Debt - 3.75% Convertible Senior Notes - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended	1 Months Ended		3 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	May 31, 2014 3.75% Convertible Senior Notes [Member]	Apr. 30, 2014 3.75% Convertible Senior Notes [Member]	Jun. 30, 2014 3.75% Convertible Senior Notes [Member]	Jun. 30, 2014 3.75% Convertible Senior Notes [Member]	Jun. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Jun. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Jun. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Sep. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member] Forecast [Member]	Jun. 30, 2014 $1 Billion Credit Facility [Member]	Dec. 31, 2013 $1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Conversion rate per $ 1,000 principal of convertible notes						47.9789
Common Stock principal amount of convertible notes					$ 1,000	$ 1,000
Conversion price per share					$ 20.84	$ 20.84
Conversion settlement amount of convertible notes						1,000
Total credit facility											1,000,000,000	1,000,000,000
Cancellation of Convertible notes				56,300,000
Aggregate consideration for cancellation of convertible notes				120,200,000
Consideration received from counter parties				9,200,000
Value of convertible notes converted by a holder						15,300,000
Consideration for convertible note conversion						33,400,000
Loss on extinguishment on debt	2,148,000	2,148,000			2,100,000	2,100,000
Reduction in stockholder's equity due to repurchase and conversion transactions			(47,200,000)		(52,000,000)	(52,000,000)	(52,300,000)
Strike price of purchased option		20.84
Purchased options number of shares	11.1	11.1
Warrants repurchased						2.4				2.4
Total consideration for repurchase of warrants		50,775,000				50,775,000
Loss on change in the fair value of the derivative liability					$ 2,500,000	$ 2,500,000		$ 2,300,000	$ 2,300,000
Approximate number of common stock share which can be purchased under warrants	9.6	9.6
Adjusted strike price under warrant	25.01	25.01