Stockholders' Equity (Narrative) (Details) (USD $)	1 Months Ended					1 Months Ended		12 Months Ended			1 Months Ended
	Apr. 30, 2011	Feb. 28, 2010	Dec. 31, 2011	Feb. 28, 2011	Dec. 31, 2010	Feb. 28, 2010 Preferred stock	Feb. 28, 2010 Series A common stock	Dec. 31, 2011 Series A common stock	Dec. 31, 2010 Series A common stock	Dec. 31, 2009 Series A common stock	Apr. 30, 2011 Quarterly [Member] Previous [Member]	Apr. 30, 2011 Quarterly [Member] Subsequent [Member]	Apr. 30, 2011 Annual [Member] Previous [Member]	Apr. 30, 2011 Annual [Member] Subsequent [Member]	Dec. 31, 2011 Senior Unsecured Notes Due 2018 [Member]	Dec. 31, 2010 Senior Unsecured Notes Due 2018 [Member]	Sep. 30, 2010 Senior Unsecured Notes Due 2018 [Member]	Dec. 31, 2011 Senior Unsecured Notes Due 2021 [Member]	May 31, 2011 Senior Unsecured Notes Due 2021 [Member]	Dec. 31, 2010 Senior Unsecured Notes Due 2021 [Member]
Dividend rate on convertible perpetual preferred stock		4.25%
Preferred stock, shares outstanding		9,600,000	0		0
Common stock received for each share of preferred stock		1.2600
Common stock, par value				$ 0.0001
Conversion of preferred stock, shares converted						9,591,276
Conversion of preferred stock, shares issued							12,084,942
Redemption of preferred stock, shares outstanding						8,724	7,437	0	(7,437)	0
Interest rate, stated percentage															6.625%	6.625%	6.625%	5.875%	5.875%	5.875%
Common Stock, Dividends, Rate Increase, Percent	20.00%
Common Stock, Dividends, Per Share, Declared											$ 0.05	$ 0.06	$ 0.2	$ 0.24