Debt (Narrative) (Details) (USD $)	3 Months Ended					3 Months Ended
	Jun. 30, 2013	Jun. 01, 2013	Mar. 31, 2013	Jun. 30, 2013 Senior Secured Revolving Credit Facility [Member]	Dec. 31, 2012 Senior Secured Revolving Credit Facility [Member]	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Maximum [Member]	Jun. 30, 2013 Convertible Senior Notes [Member]	Dec. 31, 2012 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Consideration Received For Repurchase Of Convertible Notes		$ 69,300,000
Percentage Of Convertible Notes Repurchased		94.00%
Offering Price		1,000
Principal amount per note		1,000
Convertible debt								4,425,000	73,750,000
Repurchase Price, Percentage Of Principal Amount								100.00%
Debt Instrument, Unamortized Discount								0	1,093,000
Debt instrument interest rate								4.375%
Redemption price, percentage of principal amount								100.00%
Line of credit facility, maximum borrowing capacity	750,000,000
Line of credit adjusted borrowing base			365,000,000
Line of credit facility, current borrowing capacity	530,000,000
Ratio of total debt to EBITDA	2.5						4.00
Current ratio	1.83					1.00
Ratio of senior debt to EBITDA	0.07						2.5
Ratio of EBITDA to interest expense	5.31					2.5
Line of credit facility amount outstanding				28,000,000	0
Debt, Weighted Average Interest Rate	2.19%
Letters of credit outstanding amount				$ 900,000