Long-Term Debt (Details) (USD $)			1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jan. 31, 2008 Convertible Subordinated Notes	Jun. 30, 2012 Convertible Subordinated Notes	Jun. 30, 2011 Convertible Subordinated Notes	Jun. 30, 2012 Convertible Subordinated Notes	Jun. 30, 2011 Convertible Subordinated Notes
Information related to long-term obligations
Carrying Value of convertible subordinated notes	$ 172,500,000	$ 172,500,000
Estimated Fair Value of convertible subordinated notes	183,549,000	189,588,000
Debt disclosures
Loan amount			172,500,000
Proceeds from issuance of debt, net of issuance costs			166,700,000
Interest rate (as a percent)				3.00%		3.00%
Conversion rate, number of shares to be issued per $1000 of principal amount of notes						38.6548
Principal amount used for debt instrument conversion ratio				1,000		1,000
Initial conversion price of convertible notes into common stock (in dollars per share)				$ 25.87		$ 25.87
Unamortized debt issuance costs				2,100,000		2,100,000
Amortization expense				$ 200,000	$ 200,000	$ 400,000	$ 400,000
Percentage of principal amount at which the entity may redeem some or all notes						100.00%
Percentage of closing sales price of the entity's common stock the conversion price must exceed in order for the notes to be convertible						130.00%
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable						20 days
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be redeemable						30 days