Revolving Credit Facility (Details Textual) (USD $)			9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Revolving credit facility [Member] option	Sep. 30, 2014 Common stock Class A [Member] Revolving credit facility [Member]	Sep. 30, 2014 Common stock Class A or B [Member] Revolving credit facility [Member]	Sep. 30, 2014 LIBOR [Member] Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Total available borrowings	$ 500,000,000	$ 500,000,000
Number of Credit Facility extension options			1
Term of Credit Facility extension option			12 months
Variable rate basis spread of debt instrument						3.50%
Amount of available borrowings that can be used for letters of credit and/or surety bonds			100,000,000
Maximum Class A common stock repurchase amount				100,000,000
Maximum dividend restriction in any four fiscal quarter period					$ 24,000,000