Debt (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Annual maturities of long-term debt, excluding capital lease obligations
2012	$ 0
2013	0
2014	512,180
2015	600,000
2016	0
Years thereafter	0
Total	1,112,180
$925 Million Credit Facility [Member]
Annual maturities of long-term debt, excluding capital lease obligations
2012	0
2013	0
2014	0
2015	600,000
2016	0
Years thereafter	0
Total	600,000
3.75% Convertible Senior Notes [Member]
Annual maturities of long-term debt, excluding capital lease obligations
2012	0
2013	0
2014	360,000
2015	0
2016	0
Years thereafter	0
Total	360,000
6.75% Senior Notes [Member]
Annual maturities of long-term debt, excluding capital lease obligations
2012	0
2013	0
2014	152,180
2015	0
2016	0
Years thereafter	0
Total	$ 152,180