Debt - Encore Convertible Notes (Details) $ / shares in Units, $ in Millions	Mar. 05, 2014 $ / shares	Jun. 24, 2013 $ / shares	Nov. 27, 2012 $ / shares	Sep. 30, 2015 $ / shares	Mar. 31, 2014 USD ($)	Jul. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
2017 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate				3.00%
Initial conversion price (in dollars per share)			$ 31.56	$ 31.56
Closing stock price at date of issuance (in dollars per share)			$ 25.66
Conversion rate (shares per $1,000 principal amount)			31.6832
2020 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate				3.00%
Initial conversion price (in dollars per share)		$ 45.72		$ 45.72
Closing stock price at date of issuance (in dollars per share)		$ 33.35
Conversion rate (shares per $1,000 principal amount)		21.8718
2021 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate				2.875%
Initial conversion price (in dollars per share)	$ 59.39			$ 59.39
Closing stock price at date of issuance (in dollars per share)	$ 47.51
Conversion rate (shares per $1,000 principal amount)	16.8386
Convertible Notes [Member] | 2017 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount | $							$ 115.0
Debt instrument, stated interest rate							3.00%
Convertible Notes [Member] | 2020 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount | $						$ 172.5
Debt instrument, stated interest rate						3.00%
Convertible Notes [Member] | 2021 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount | $					$ 161.0
Debt instrument, stated interest rate					2.875%