Earnings Per Share (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended									1 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2014 4.0% Convertible Notes [Member] Common Stock [Member]	Jun. 30, 2014 2011 4.0% Notes [Member] Common Stock [Member]	Jun. 30, 2014 2009 4.0% Notes [Member] Common Stock [Member]	Sep. 30, 2014 Unsecured Debt [Member] 4.0% Convertible Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] 2011 4.0% Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] 2009 4.0% Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] 4.25% Convertible Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] 2011 4.25% Notes [Member]	Sep. 30, 2014 Unsecured Debt [Member] 2009 4.25% Notes [Member]	Jun. 30, 2014 Convertible Debt [Member] 2011 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] 2011 4.25% Notes [Member]	Sep. 30, 2013 Convertible Debt [Member] 2011 4.25% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] 2011 4.25% Notes [Member]	Sep. 30, 2013 Convertible Debt [Member] 2011 4.25% Notes [Member]	Sep. 30, 2013 Convertible Debt [Member] 2011 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] 2011 4.0% Notes [Member]	Sep. 30, 2013 Convertible Debt [Member] 2011 4.0% Notes [Member]	Jun. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 4.0% Convertible Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 4.0% Convertible Notes [Member]	Jun. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.0% Notes [Member]	Jun. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.0% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 4.25% Convertible Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2011 4.25% Notes [Member]	Sep. 30, 2014 Convertible Debt [Member] Unsecured Debt [Member] 2009 4.25% Notes [Member]
Earnings Per Share [Line Items]
Principal amount																												$ 100,000,000	$ 97,000,000	$ 3,000,000
Debt instrument, convertible, interest rate																							4.00%		4.00%		4.00%	4.25%	4.25%	4.25%
Debt instrument, convertible, matured and converted																						115,000,000		105,300,000		9,600,000
Debt instrument, settlement in cash			$ 105,325,000	$ 150,000,000										$ 105,300,000
Debt instrument, convertible, common shares issued					4,200,000	3,600,000	600,000
Debt instrument, convertible, conversion price per share								$ 15.76	$ 15.76	$ 15.76	$ 15.48	$ 15.48	$ 15.48
Premium shares															3,005,000	3,314,000	3,501,000	3,097,000	3,476,000	2,400,000	3,240,000
Weighted average anti-dilutive common stock equivalents, shares	304,486	0	223,422	0