Debt (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	9 Months Ended			1 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Aug. 31, 2013 Senior Convertible Notes	Sep. 30, 2013 Senior Convertible Notes	Sep. 30, 2013 Senior Convertible Notes Note Hedges	Sep. 30, 2013 Senior Convertible Notes Warrant [Member]	Sep. 30, 2013 After December 31, 2013 [Member] Senior Convertible Notes D	Sep. 30, 2013 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	731,000			111,500,000	112,302,000
Additional paid in capital				38,500,000
Transaction costs					4,900,000
Debt component of transaction costs, gross				3,600,000
Deferred debt issuance costs, net	3,535,000		71,000
Transaction costs, additional paid in capital				1,300,000
Net proceeds from the Notes					145,100,000
Payments of convertible note hedges	31,408,000	0				31,400,000
Proceeds from the issuance of warrants	$ 21,763,000	$ 0					$ 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