Long-Term Debt - Convertible Notes (Details)	1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 30, 2014 USD ($) shares	Sep. 30, 2014 shares	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2009 USD ($) $ / shares
Debt Instrument [Line Items]
Value of shares acquired upon exercise of call options			$ 0	$ 89,407,000
4.25% convertible senior notes due June 2014
Debt Instrument [Line Items]
Principle amount of senior notes					$ 355,000,000.0
Interest rate (as a percent)	4.25%				4.25%
Conversion rate of debt instrument (Shares per USD)	0.0435084
Conversion price per common stock shares (in dollars per share) | $ / shares					$ 22.98
Repayment of long term debt	$ 370,000,000
Number of shares of common stock issued upon redemption of debt | shares	6,800,000
Price per share of common stock for call options purchased (in dollars per share) | $ / shares					22.98
Warrant exercise price (in dollars per share) | $ / shares					32.19
Effective conversion price (in dollars per share) | $ / shares					$ 32.19
Debt instrument face amount for effective conversion price					$ 325,000,000
Number of shares acquired upon exercise of call options | shares	6,500,000
Value of shares acquired upon exercise of call options	$ 89,400,000
Trading days within which counterparties have the right to exercise warrants	80 days
4.25% convertible senior notes due June 2014 | Warrant
Debt Instrument [Line Items]
Common shares issued out of treasury stock | shares		498,254