Debt (Narrative) (Details) (USD $)	1 Months Ended	12 Months Ended							12 Months Ended															1 Months Ended
	May 21, 2008	Dec. 31, 2013	Oct. 30, 2013	Sep. 30, 2013	Jun. 01, 2013	Nov. 30, 2010	Dec. 31, 2013 Senior Secured Revolving Credit Facility [Member]	Dec. 31, 2012 Senior Secured Revolving Credit Facility [Member]	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2013 Prior to September 15, 2015 [Member]	Dec. 31, 2013 8.625% Senior Notes [Member]	Nov. 17, 2011 8.625% Senior Notes [Member]	Nov. 02, 2010 8.625% Senior Notes [Member]	Dec. 31, 2013 8.625% Senior Notes [Member] On and after October 15, 2014 [Member]	Dec. 31, 2013 8.625% Senior Notes [Member] On and after October 15, 2014 [Member] Minimum [Member]	Dec. 31, 2013 8.625% Senior Notes [Member] Prior to October 15, 2014 [Member]	Dec. 31, 2013 7.50% Senior Notes [Member]	Sep. 10, 2012 7.50% Senior Notes [Member]	Dec. 31, 2013 7.50% Senior Notes [Member] On and after September 15, 2016 [Member] Minimum [Member]	Dec. 31, 2013 7.50% Senior Notes [Member] On and after September 15, 2016 [Member] Maximum [Member]	Dec. 31, 2013 7.50% Senior Notes [Member] October Fifteen Two Thousand And Thirteen [Member]	Dec. 31, 2013 7.50% Senior Notes [Member] Prior to September 15, 2016 [Member]	May 21, 2008 4.375% Convertible Senior Notes [Member] Rate	Nov. 30, 2010 4.375% Convertible Senior Notes [Member]	Dec. 31, 2013 Convertible Senior Notes [Member]	Dec. 31, 2012 Convertible Senior Notes [Member]	May 21, 2008 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate														8.625%				7.50%								4.375%
Aggregate principal amount													$ 200,000,000	$ 400,000,000					$ 300,000,000									$ 373,800,000.0
Redemption price, percentage of principal amount											107.50%				104.313%	100.00%	100.00%			100.00%	103.75%		100.00%			100.00%
Change of control repurchase price percentage												101.00%						101.00%
Debt instrument redemption, percentage of principal																						35.00%
Tender Offer Amount For Convertible Senior Notes																									300,000,000
Convertible Debt																										4,425,000	73,750,000
Consideration Paid For Repurchase Of Convertible Notes					69,300,000
Principal amount per note						1,000
Debt Instrument, Convertible, Conversion Ratio																								9.9936
Debt Instrument, Convertible, Conversion Price																								$ 100.06
Convert If Stock Price Exceeds Percentage	130.00%
Convert if trading price equal to or less than percentage																								97.00%
Repurchase Price, Percentage Of Principal Amount																										100.00%
Line of credit facility, maximum borrowing capacity		1,000,000,000		750,000,000
Line of credit facility current borrowing base		470,000,000
Federal funds rate plus percentage		0.50%
Adjusted LIBO rate plus percentage		1.00%
Additional margin, percent									0.50%	1.50%
Additional margin for Eurodollar loans, percent									1.50%	2.50%
Line of Credit Facility, Previous Borrowing Capacity			530,000,000
Ratio of total debt to EBITDA		1.94								4.00
Current ratio		2.57							1.00
Line of credit facility amount outstanding							0	0
Letters of credit outstanding amount							$ 900,000