Debt - 3.75% Convertible Senior Notes - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended				1 Months Ended		3 Months Ended	6 Months Ended	9 Months Ended		1 Months Ended		3 Months Ended	9 Months Ended	0 Months Ended
	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 $1 Billion Credit Facility [Member]	Dec. 31, 2013 $1 Billion Credit Facility [Member]	Jun. 30, 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]	Sep. 30, 2014 3.75% Convertible Senior Notes [Member]	Sep. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Paid-in Capital [Member]	Sep. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Aug. 31, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Sep. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Sep. 30, 2014 3.75% Convertible Senior Notes [Member] Additional Warrant [Member]	Oct. 01, 2014 3.75% Convertible Senior Notes [Member] Subsequent Event [Member]	Oct. 01, 2014 3.75% Convertible Senior Notes [Member] Subsequent Event [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
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
Loss on extinguishment on debt	4,181,000	2,148,000	4,181,000							2,100,000
Reduction in stockholder's equity due to repurchase and conversion transactions										(52,000,000)	(47,200,000)	(52,300,000)
Conversion settlement amount of convertible notes																1,000
Conversion of shares, stock issued																6.3
Total credit facility				1,000,000,000	1,000,000,000
Strike price of purchased option		$ 20.84
Purchased options number of shares		11.1
Warrants repurchased						2.4							2.4
Total consideration for repurchase of warrants		108,331,000				50,800,000							57,600,000
Loss on change in the fair value of the derivative liability								$ 2,300,000		$ 2,500,000				$ 1,600,000	$ 1,600,000
Approximate number of common stock share which can be purchased under warrants		7.2
Adjusted strike price under warrant		$ 25.01