Shareholders' Equity (Narrative) (Details) (USD $) In Millions, unless otherwise specified			0 Months Ended	6 Months Ended
Jun. 30, 2014 1.875% Convertible Senior Notes [Member]	Jun. 30, 2014 4.0% Convertible Senior Notes [Member]	Apr. 29, 2009 4.0% Convertible Senior Notes [Member]	Apr. 27, 2011 Current Stock Repurchase Program [Member] Class A Common Stock [Member]	Jun. 30, 2014 Current Stock Repurchase Program [Member] Class A Common Stock [Member]
Class of Stock [Line Items]
Debt instrument stated percentage	1.875%	4.00%	4.00%
Stock repurchase program, authorized				$ 300.0	$ 300.0
Stock repurchase program, remaining authorization					$ 150.0

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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