Convertible Notes (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest expense related to notes
Total interest expense on convertible notes	$ 27,510	$ 24,828	$ 20,228
Adjustment to interest expense due to incorrect amortization of the non-cash debt discount			700
Zero Coupon Convertible Senior Notes due 2010
Interest expense related to notes
Amortization of discount at an additional effective interest rate	0	0	958
Effective interest rate (as a percent)			8.40%
Convertible notes
Interest expense related to notes
Total interest expense on convertible notes	23,320	21,247	19,699
5% Convertible Senior Notes due 2014
Interest expense related to notes
2014 Notes coupon interest at a rate of 5%	8,625	8,625	8,625
Amortization of discount at an additional effective interest rate	$ 14,695	$ 12,622	$ 10,116
Effective interest rate (as a percent)	11.70%	11.70%	11.70%