Convertible Senior Notes due 2016 (Details Textuals) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2011	Aug. 31, 2009
Convertible Senior Notes due 2016 (Textuals) [Abstract]
Aggregate principal amount of senior notes due 2016			$ 230,000,000
Rate of Convertible senior notes due 2016	4.00%	4.00%
2016 Notes interest rate per year		4.00%
Conversion rate (shares of common stock per $1,000 principal amount of debentures)		25.2207
Conversion price (per share of common stock)	$ 39.65	$ 39.65
Principal amount repurchase percentage	100.00%	100.00%
Principal amount per debenture used in conversion rate		1,000
Redemption provisions		The Company may redeem all or part of the outstanding 2016 notes provided that the last reported sale price of the common stock for 20 or more trading days in a period of 30 consecutive trading days ending on the trading day prior to the date the Company provides the notice of redemption to holders of the 2016 Notes exceeds 130% of the conversion price in effect on each such trading day.
Principal amount redeemed percentage	100.00%	100.00%
Effective interest rate	12.50%	12.50%
Equity component of convertible debt	89,468,000	89,468,000
Cash interest expense on debt	2,300,000	4,600,000
Non-cash interest expense relating to amortization of the debt discount	2,500,000	4,900,000
Estimated fair value of senior notes	$ 271,400,000	$ 271,400,000

Convertible senior notes due 2016.

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