Debt, Textuals (Details) (USD $)	3 Months Ended	6 Months Ended							3 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Convertible Notes	Mar. 29, 2010 Convertible Notes	Jun. 30, 2012 Call Options	Jun. 30, 2012 Warrant Transactions	May 23, 2012 Senior Notes	Jun. 30, 2012 Minimum	Jun. 30, 2012 On or after June 1, 2016 Senior Notes	Jun. 30, 2012 Prior to June 1, 2015 Senior Notes	Jun. 30, 2012 On or after June 1, 2015 but prior to June 1, 2016 Senior Notes	Jun. 30, 2012 Change in control Senior Notes
Debt Instruments
Aggregate principal amount of notes					$ 175,000,000			$ 225,000,000
Interest rate					4.50%			8.25%
Effective interest rate					11.00%
Capitalized deferred financing costs					5,900,000			6,400,000
Price as percentage of principal amount of notes plus any accrued and unpaid interest for repurchase of notes				100.00%						104.125%	108.25%	100.00%	101.00%
Percentage of principal amount of Notes that may be redeemed											35.00%
Payment of quarterly cash dividends	$ 0.25	$ 0.50	$ 0.48						$ 0.24
Conversion rate of common stock shares per $1,000 of principal amount				20.7076
Principal amount in conversion feature				$ 1,000
Conversion price of note	$ 48.29	$ 48.29
Stock price threshold for conversion of notes	$ 62.78	$ 62.78
Number of trading days within 30 consecutive trading days	20	20
Number of consecutive trading days within a calendar quarter	30	30
Exercise price of call options						$ 48.29
Common stock sold related to option counterparties net share-settled warrants							3,600,000
Exercise price per share on August 15, 2012							61.32