Stockholders' Equity, Convertible Preferred Stock (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock, shares outstanding (shares)	7,252,000	7,252,000	7,252,000	7,252,000
5.75% Cumulative Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Preferred stock, shares outstanding (shares)	1,497,000	1,497,000	1,497,000	1,497,000
5.75% Cumulative Convertible Preferred Stock Series A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Preferred stock, shares outstanding (shares)	1,100,000	1,100,000	1,100,000	1,100,000
4.50% Cumulative Comvertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 100
Preferred stock, shares outstanding (shares)	2,559,000	2,559,000	2,559,000	2,559,000
5.0% Cumulative Convertible Preferred Stock Series Two Thousand And Five B [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 100
Preferred stock, shares outstanding (shares)	2,096,000	2,096,000	2,096,000	2,096,000