Debt, Textuals (Details) (USD $)	3 Months Ended	9 Months Ended			1 Months Ended	9 Months Ended	12 Months Ended							9 Months Ended		3 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Nov. 15, 2012	Oct. 31, 2012 Convertible Notes	Sep. 30, 2012 Convertible Notes	Dec. 31, 2010 Convertible Notes	Nov. 15, 2012 Convertible Notes	Mar. 29, 2010 Convertible Notes	Nov. 15, 2012 Call Options	Sep. 30, 2012 Call Options	Nov. 15, 2012 Warrant Transactions	Sep. 30, 2012 Warrant Transactions	Sep. 30, 2012 Senior Notes	May 23, 2012 Senior Notes	Sep. 30, 2012 Minimum	Sep. 30, 2012 On or after June 1, 2016 Senior Notes	Sep. 30, 2012 Prior to June 1, 2015 Senior Notes	Sep. 30, 2012 On or after June 1, 2015 but prior to June 1, 2016 Senior Notes	Sep. 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%
Transaction fees capitalized		6,600,000	2,100,000				5,900,000							6,600,000
Redemption price of debt as a percentage of principal amount						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	$ 0.75	$ 0.72													$ 0.24
Conversion rate of common stock shares per $1,000 of principal amount					20.7111	20.7076
Principal amount in conversion feature								$ 1,000
Conversion price of note	$ 48.29	$ 48.29		$ 48.28
Stock price threshold for conversion of notes						$ 62.78
Number of trading days within 30 consecutive trading days						20
Number of consecutive trading days within a calendar quarter						30
Exercise price of call options										$ 48.28	$ 48.29
Common stock sold related to option counterparties net share-settled warrants													3,600,000
Exercise price per share of Warrants												61.31	61.32