Long-Term Debt, Textuals (Details) (USD $)	3 Months Ended	12 Months Ended				1 Months Ended	3 Months Ended	12 Months Ended							12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 15, 2013	Feb. 15, 2013 Convertible Notes	Mar. 31, 2010 Convertible Notes	Dec. 31, 2012 Convertible Notes	Mar. 29, 2010 Convertible Notes	Feb. 15, 2013 Call Options	Dec. 31, 2012 Call Options	Feb. 15, 2013 Warrant Transactions	Dec. 31, 2012 Warrant Transactions	Mar. 30, 2010 Warrant Transactions	Dec. 31, 2012 Senior Notes	May 23, 2012 Senior Notes	Dec. 31, 2012 Minimum	Dec. 31, 2012 On or after June 1, 2016 Senior Notes	Dec. 31, 2012 Prior to June 1, 2015 Senior Notes	Dec. 31, 2012 On or after June 1, 2015 but prior to June 1, 2016 Senior Notes	Dec. 31, 2012 Change in control Senior Notes
Debt Instruments
Principal amount of notes	$ 225,000,000	$ 225,000,000	$ 0						$ 175,000,000							$ 225,000,000
Interest rate									4.50%							8.25%
Transaction fees capitalized as deferred financing costs		6,600,000	2,100,000	8,600,000			5,900,000								6,600,000
Interest expense															11,800,000
Interest expense related to amortization of financing costs															500,000
Effective interest rate								11.00%							8.60%
Redemption price of debt as a percentage of principal amount									100.00%									104.125%	108.25%	100.00%	101.00%
Conversion percentage threshold of stock price over conversion price								130.00%
Percentage of principal amount of Notes that may be redeemed																			35.00%
Payment of quarterly cash dividends	$ 0.25	$ 1.00	$ 0.96	$ 0.96													$ 0.24
Conversion rate of common stock shares per $1,000 of principal amount						20.7309		20.7111
Principal amount in conversion feature						$ 1,000		$ 1,000
Conversion price of note	$ 48.28	$ 48.28			$ 48.24
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										$ 48.24	$ 48.28
Common stock sold related to option counterparties net share-settled warrants													3,600,000	3,600,000
Exercise price per share of Warrants												61.25	61.31