Summary of Significant Accounting Policies Diluted Earnings Per Share (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share, Diluted, by Common Class [Line Items]
Net income (loss)	$ 3,895	$ 30,301	$ (3,795)	$ 49,674
Net income (loss) available to common stockholders	3,816	29,569	(3,795)	50,458
Variable Interest 3.875% Senior Convertible Debentures [Member]
Earnings Per Share, Diluted, by Common Class [Line Items]
Income attributable to 3.875% Variable Interest Senior Convertible Debentures	0	(95)	0	0
Variable Interest 6.75% Senior Convertible Debentures [Member]
Earnings Per Share, Diluted, by Common Class [Line Items]
Expense attributable to 6.75% Variable Interest Senior Convertible Note	0	0	0	1,856
Earnings Per Share, Diluted [Member]
Earnings Per Share, Diluted, by Common Class [Line Items]
Income (expense) attributable to participating securities	$ (79)	$ (637)	$ 0	$ (1,072)