Fair Value Measurements (Details Textual) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012 Securities	Dec. 31, 2011 Securities
Debt Instrument [Line Items]
Percentage of auction rate securities within the investment portfolio	less than one percent	less than one percent
Fair Value Measurements (Textual) [Abstract]
Transfers between levels	$ 0	$ 0
Number of auction rate securities	2	3
7.5% Senior Notes, due November 15, 2019 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.50%	7.50%
2.0% Convertible Senior Notes, due May 15, 2012 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.00%	2.00%