Debt - Narrative (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	9 Months Ended		1 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Aug. 31, 2013 Senior Convertible Notes	Sep. 30, 2014 Senior Convertible Notes	Sep. 30, 2014 Senior Convertible Notes Note Hedges	Sep. 30, 2014 Senior Convertible Notes Warrant [Member]	Sep. 30, 2014 After December 31, 2013 [Member] Senior Convertible Notes D	Sep. 30, 2014 Warrant [Member]
Debt Instrument [Line Items]
Proceeds from issuance of debt			$ 150,000,000
Interest rate				1.50%
Conversion ratio				0.061677
Conversion price				$ 16.21
Threshold trading days							20
Threshold consecutive trading days				5 days			30 days
Threshold percentage of stock price trigger				98.00%			130.00%
Threshold business days				5 days
Cash repurchase price, percent				100.00%
Minimum percent held in principal amount of outstanding notes to declare all notes to be due and payable				25.00%
Debt	1,161,000		111,500,000	118,958,000
Additional paid in capital			38,500,000
Transaction costs				4,900,000
Debt component of transaction costs, gross			3,600,000
Transaction costs, additional paid in capital			1,300,000
Net proceeds from the Notes				145,100,000
Payments of convertible note hedges	0	31,408,000			31,400,000
Proceeds from the issuance of warrants	$ 0	$ 21,763,000				$ 21,800,000		$ 21,800,000
Shares covered under note hedges		9.25
Warrants sold to acquire shares								9.25
Exercise price of warrant								21.02
Common stock strike price		$ 16.21