Debt - Summary of Debt and Capital Lease Obligations (Parenthetical) (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
3.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate of Senior Notes	3.75%	3.75%
Maturity date for Notes	Oct. 01, 2014	Oct. 01, 2014
Debt discount on Convertible Senior Notes	$ 0	$ 10,096,000
$1 Billion Credit Facility [Member]
Debt Instrument [Line Items]
Total credit facility	1,000,000,000	1,000,000,000
Spread rate added to LIBOR	1.85%	1.85%
Maturity date for credit facility	Apr. 18, 2017	Apr. 18, 2017
$400 Million Term Loan Facility [Member]
Debt Instrument [Line Items]
Total credit facility	$ 400,000,000
5% Senior Notes [Member]
Debt Instrument [Line Items]
Interest rate of Senior Notes	5.00%	5.00%
Maturity date for Notes	Apr. 15, 2021	Apr. 15, 2021