Debt and Other Financing Arrangements Debt - Additional Information (Details) (USD $)	0 Months Ended	12 Months Ended					0 Months Ended		0 Months Ended		1 Months Ended
	Jun. 17, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Other Debt Arrangements	Dec. 31, 2012 Other Debt Arrangements	Jun. 17, 2013 Convertible Debt	Dec. 31, 2013 Convertible Debt	Jun. 17, 2013 Prior to April 1, 2018 Maximum Convertible Debt trading_day	Jun. 17, 2013 Prior to April 1, 2018 Minimum Convertible Debt trading_day	Jun. 30, 2013 Silicon Valley Bank Amended Line of Credit	Nov. 30, 2012 Silicon Valley Bank Amended Line of Credit
Debt Instrument [Line Items]
Short-term Debt, Weighted Average Interest Rate		7.00%	5.20%
Proceeds from Issuance of Long-term Debt							$ 246,000,000
Debt Instrument, Face Amount							253,000,000
Debt Instrument, Interest Rate, Stated Percentage							1.50%
Debt Instrument, Convertible, Conversion Ratio							18.5046
Debt Instrument, Convertible, Conversion Price	$ 54.04
Debt Instrument, Convertible, Threshold Trading Days									20	5
Debt Instrument, Convertible, Threshold Consecutive Trading Days									30 days	5 days
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger									130.00%	98.00%
Convertible Debt							214,300,000	217,965,000
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt		11,282,000					38,700,000
Debt Issuance Cost							7,300,000
Unamortized Debt Issuance Expense							6,200,000
Debt Instrument, Convertible, Issuance Cost Allocated to Equity Components							1,100,000
Payments for Derivative Instrument, Financing Activities	49,500,000	49,537,000	0	0
Derivative, Nonmonetary Notional Amount, Number of Shares	4,700,000
Proceeds from the issuance of warrants		23,225,000	0	0
Number of shares purchasable upon warrant exercise		4,700,000
Warrants exercise price (in usd per share)		80.06
Line of Credit Facility, Maximum Borrowing Capacity												5,000,000
Repayments of Lines of Credit											3,000,000
Debt Instrument, Amount Outstanding					900,000	1,400,000
Debt Instrument, Fair Value Disclosure		$ 900,000	$ 1,400,000