Earnings Per Share Additional Information (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Apr. 24, 2014	Sep. 30, 2014 2017 Convertible Senior Notes [Member]	Dec. 31, 2012 2017 Convertible Senior Notes [Member]	Nov. 27, 2012 2017 Convertible Senior Notes [Member]	Dec. 31, 2012 2017 Convertible Senior Notes [Member] Before Amendment [Member]	Dec. 16, 2013 2017 Convertible Senior Notes [Member] After Amendment [Member]	Sep. 30, 2014 2017 Convertible Senior Notes [Member] Adjusted Debt Conversion Rate Following Hedge Transactions [Member]	Sep. 30, 2014 2020 Convertible Senior Notes [Member]	Jun. 24, 2013 2020 Convertible Senior Notes [Member]	Sep. 30, 2014 2021 Convertible Senior Notes [Member]	Mar. 05, 2014 2021 Convertible Senior Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock repurchase program, amount authorized						$ 50,000,000.0
Stock repurchased during period (shares)	400,000
Stock repurchased during period (value)	16,800,000
Anti-dilutive securities, employee stock options excluded from EPS		0	0	0	0
Debt component							$ 115,000,000						$ 172,500,000		$ 161,000,000
Initial conversion price							$ 31.56		$ 31.56			$ 60.00	$ 45.72	$ 45.72	$ 59.39	$ 59.39
Warrants sold to purchase common stock (in shares)								3,600,000
Warrants exercise price (in dollars per share)										$ 44.19	$ 60.00