Debt (4.0% Convertible Senior Notes Due 2014) (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended			0 Months Ended	3 Months Ended	6 Months Ended	0 Months Ended	3 Months Ended	6 Months Ended			6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Class A Common Stock [Member]	Apr. 29, 2009 4.0% Convertible Senior Notes [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member]	Apr. 24, 2009 4.0% Convertible Senior Notes [Member] Class A Common Stock [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member] Class A Common Stock [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member] Class A Common Stock [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member] Minimum [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member] Maximum [Member]	Jun. 30, 2014 Subsequent Event [Member]	Jun. 30, 2014 Subsequent Event [Member] Class A Common Stock [Member]	Jun. 30, 2014 Subsequent Event [Member] 4.0% Convertible Senior Notes [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	4,278,000	3,923,000	8,516,000	7,527,000		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%	12.80%
Carrying amount of the equity component							166,900,000	166,900,000
Trading days										20 days	20 days
Consecutive trading days										30 days	30 days
Common stock closing price per share										$ 39.49	$ 39.49
Principal amount converted							121,500,000	121,600,000
Issuance of common stock										2,700,000	2,700,000
Common stock received from conversion settlement											2,700,000					100,000
Additional conversion notices aggregate value								11,300,000
Company paid in cash to settle warrants			$ 276,227,000	$ 23,648,000										$ 66,500,000
Settlement of outstanding warrants, percentage			30.00%											7.50%
Settlement of convertible notes, Shares					4,900,000										1,200,000
Settlement trading days								60 days
Number of warrants remaining under obligation								10,300,000