Debt Convertible Senior Notes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 08, 2014
Debt Instrument [Line Items]
Proceeds from issuance of convertible senior notes	$ 172,500,000	$ 0	$ 0
Other Current Assets [Member]
Debt Instrument [Line Items]
Deferred financing costs	300,000
Other non-current assets [Member]
Debt Instrument [Line Items]
Deferred financing costs	500,000	1,200,000
3.25% Convertible Senior Notes due 2020 [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Convertible Senior Notes, face amount	172,500,000			172,500,000
Convertible Senior Notes, interest rate, stated percentage	3.25%
Debt issuance cost	5,100,000
Deferred financing costs	4,200,000
Remaining amortization period of discount on the liability component	6 years 0 months 0 days
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs	900,000
Convertible Senior Notes, conversion ratio	31.1891
Convertible Senior Notes, conversion price	$ 32.06
Convertible Senior Notes, threshold trading days	20
Convertible Senior Notes, threshold consecutive trading days	30 years 0 months 0 days
Convertible Senior Notes, threshold percentage of stock price trigger	130.00%
Convertible Senior Notes, threshold consecutive business days	5 years 0 months 0 days
Debt Instrument, Convertible, Threshold Consecutive Trading Days, Following Consecutive Business Days	5 years 0 months 0 days
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger, Following Consecutive Business Days	98.00%
Convertible Senior Notes, observation period	25 years 0 months 0 days
Carrying value of equity component, net of issuance costs	29,758,000			30,700,000
Interest expense, Convertible Senior Notes, Amortization	300,000
Interest expense, Convertible Senior Notes	300,000
Convertible Senior Notes, fair value disclosures				141,900,000
Proceeds from issuance of convertible senior notes	172,500,000
3.25% Convertible Senior Notes due 2020 [Member] | Other Current Assets [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Deferred financing costs	600,000
3.25% Convertible Senior Notes due 2020 [Member] | Other non-current assets [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
Deferred financing costs	$ 3,500,000