Debt (4.0% Convertible Senior Notes Due 2014) (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 29, 2009 4.0% Convertible Senior Notes [Member]	Dec. 31, 2013 4.0% Convertible Senior Notes [Member]	Dec. 31, 2013 4.0% Convertible Senior Notes [Member]	Apr. 24, 2009 4.0% Convertible Senior Notes [Member] Class A Common Stock [Member]	Dec. 31, 2013 4.0% Convertible Senior Notes [Member] Class A Common Stock [Member]	Dec. 31, 2013 4.0% Convertible Senior Notes [Member] Minimum [Member]	Dec. 31, 2013 4.0% Convertible Senior Notes [Member] Maximum [Member]	Dec. 31, 2013 Circumstance A [Member] 4.0% Convertible Senior Notes [Member] Class A Common Stock [Member]	Dec. 31, 2013 Circumstance A [Member] 4.0% Convertible Senior Notes [Member] Minimum [Member] Class A Common Stock [Member]	Dec. 31, 2013 Circumstance B [Member] Class A Common Stock [Member]	Dec. 31, 2013 Circumstance B [Member] Maximum [Member] Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, issuance date				Apr. 24, 2009
Convertible senior notes issued				$ 500,000,000
Debt instrument, interest rate, stated percentage				4.00%	4.00%	4.00%
Interest payable dates				April 1 and October 1
Debt instrument, maturity date				Oct. 01, 2014		Oct. 01, 2014
Issuance fee of convertible senior notes				11,700,000
Amortized deferred financing fees	15,560,000	12,870,000	9,188,000	7,700,000
Financing fees recorded as a reduction to shareholders' equity				4,000,000
Conversion rate							0.0329164
Per share conversion price							$ 30.38
Conversion premium							22.50%
Last reported selling price							$ 24.80
Upper strike price of warrants							$ 44.64
Coupon rate of notes									4.00%	12.90%
Carrying amount of the equity component					169,000,000	169,000,000
Convertible notes conversion criteria associated with common stock trading price						during any calendar quarter, if the last reported sale price of the Class A common stock for at least 20 trading days in the 30 consecutive trading day period ending on the last trading day of the preceding calendar quarter is more than 130% of the applicable conversion price per share of Class A common stock on the last day of such preceding calendar quarter
Convertible notes conversion criteria associated with common stock and convertible notes trading price						during the five business day period after any ten consecutive trading day period in which the trading price per $1,000 principal amount of the 4.0% Notes for each day in the measurement period was less than 95% of the product of the last reported sale price of the Class A common stock and the applicable conversion rate
Trading days								20 days			20 days
Consecutive trading days								30 days			30 days		10 days
Threshold percentage of stock trigger price												130.00%
Measurement period													5 days
Measurement period threshold percentage														95.00%
Common stock closing price per share								$ 39.49
Principal amount converted						43,000
Issuance of common stock								1,404
Common stock received								641
Additional conversion notices aggregate value					$ 33,000