Long -Term Debt (Details Textual) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			12 Months Ended
	Dec. 31, 2011 2.0% Convertible Senior Notes due May 15, 2012 [Member] M	Dec. 31, 2010 2.0% Convertible Senior Notes due May 15, 2012 [Member]	Mar. 22, 2007 2.0% Convertible Senior Notes due May 15, 2012 [Member]	Dec. 31, 2011 7.5% Senior Notes due November 15, 2019 [Member]	Jan. 18, 2012 7.5% Senior Notes due November 15, 2019 [Member]	Nov. 16, 2011 7.5% Senior Notes due November 15, 2019 [Member]
Debt Instrument [Line Items]
Principal amount of additional notes issued					$ 75,000
Principle amount applied to initial conversion ratio	1
Percentage of senior notes that may be redeemed upon an equity offering by the Company prior to November 15, 2014				35.00%
Semi-annual interest payment due dates	May 15 and November 15			May 15 and November 15
Interest payment commencement date				2012-05-15
Date up to which all or part of the notes may be redeemed at par plus accrued and unpaid interest plus a premium as determined by the indenture				2015-11-15
Date of the indenture associated with the notes				2011-11-16
Date upon which all or part of the notes may be redeemed at the redemption prices set forth in the indenture and expressed as percentages of the principal amount, plus accrued and unpaid interest				On or after November 15, 2015
Filing date of automatic registration statement on Form S-3 covering the resale of the convertible senior notes and common stock issuable upon conversion	May 2007
Redemption price percentage based on the principal amount upon an equity offering by the Company prior to November 15, 2014, plus accrued and unpaid interest				107.50%
Long-term debt, principal outstanding	259,880	260,000		400,000	475,000	400,000
Convertible senior notes issuance date	issued March 28, 2007
Convertible senior notes due date	May 15, 2012
Convertible senior notes carrying amount	256,995	245,750
Unamortized discount of debt instruments	2,885	14,250
Remaining amortization period of the unamortized discount (in months)	5
Initial conversion ratio into shares of common stock per note converted	23.5114
Conversion Price Per Share	$ 42.53
Conversion premium	32.50%
Closing price of Company's common stock	$ 59.08		$ 32.10
If-converted value per dollar above the conversion price	6,100
Average market price of the Company's common stock	$ 56.67
Aggregate principal amount of convertible notes converted	120
Conversion value in excess of the principal amount	82
Shares of common stock covered under convertible note hedge transaction	6,112,964
Shares of common stock covered under warrants	6,112,964
Strike price of warrants	$ 53.77
If-settled value per dollar above the warrant exercise price	6,100
Amount by which the if-converted value exceeds its principal amount at the balance sheet date	101,107
Amount owed to Company under hedges in cash or shares of its common stock if notes are converted	101,107
Value of common stock owed to warrant holders if warrants are exercised	32,460
Shares of common stock owed to warrant holders if warrants are exercised	549,000
Nonconvertible debt borrowing rate	6.74%
Amount of proceeds from issuance of the convertible debt allocated to equity	$ 50,885