Shareholders' Equity (Narrative) (Details) (USD $)	1 Months Ended											1 Months Ended
	Apr. 30, 2011	Feb. 28, 2010	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 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]	Jun. 30, 2011 Senior Unsecured Notes Due 2021 [Member]	May 31, 2011 Senior Unsecured Notes Due 2021 [Member]	May 06, 2011 Senior Unsecured Notes Due 2021 [Member]	Dec. 31, 2010 Senior Unsecured Notes Due 2021 [Member]	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]	Feb. 28, 2010 Preferred stock	Feb. 28, 2010 Series A common stock
Dividend rate on convertible perpetual preferred stock		4.25%
Preferred stock called for redemption		9,600,000	0	0
Common stock received for each share of preferred stock		1.26
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
Preferred stock, shares, outstanding		9,600,000	0	0
Interest rate, stated percentage					6.625%	6.625%	6.625%	5.875%	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