Debt - Hedges and EPS Impact for Convertible Notes (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended			1 Months Ended	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013 D	Feb. 28, 2014	Dec. 31, 2014	Dec. 31, 2013	Nov. 27, 2012	Jun. 24, 2013	Mar. 05, 2014	Dec. 16, 2013
Debt Instrument [Line Items]
Reclassifications of equity to temporary equity, debt conversion	$ 8,400,000
Dilutive effect of convertible senior notes	874	1,461
2017 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Cost of the hedge transaction(s)	50,595,000
Conversion price (in dollars per share)	$ 31.56						$ 31.56
Convertible debt, threshold of stock price trigger (percent)			130.00%
Convertible debt, threshold trading days			20
Convertible debt, threshold consecutive trading days			30 days
Convertible notes, fair value	157,000,000
Dilutive effect of convertible senior notes	900	1,300
2020 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Cost of the hedge transaction(s)	18,113,000
Conversion price (in dollars per share)	$ 45.72							$ 45.72
2021 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Cost of the hedge transaction(s)	19,545,000
Conversion price (in dollars per share)	$ 59.39								$ 59.39
Hedging of Convertible Debt Instrument [Member] | 2017 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Cost of the hedge transaction(s)				$ 27,900,000	$ 25,200,000	$ 2,700,000
Conversion price (in dollars per share)	$ 60.00						$ 44.19			$ 60.00
Hedging of Convertible Debt Instrument [Member] | 2020 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Conversion price (in dollars per share)	$ 61.55
Hedging of Convertible Debt Instrument [Member] | 2021 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Conversion price (in dollars per share)	$ 83.14