Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Total long-term debt	$ 656,995	$ 245,750
Current portion of long-term debt	256,995	0
Long-term debt	400,000	245,750
2.0% Convertible Senior Notes due May 15, 2012 [Member]
Debt Instrument [Line Items]
Total long-term debt	256,995	245,750
Current portion of long-term debt	256,995	0
7.5% Senior Notes due November 15, 2019 [Member]
Debt Instrument [Line Items]
Total long-term debt	$ 400,000	$ 0