Shareholder's Equity (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 31, 2010 Common Class A	Dec. 31, 2012 Common Class A	Dec. 31, 2012 Common Class B	Dec. 31, 2011 Common Class B	Dec. 31, 2012 Dividend payments limited by covenants in Credit Facility	Dec. 31, 2012 Dividend payments limited by covenants in Indentures
Shareholder's Equity
Common Stock, voting rights (votes per share)					1	.95
Per share liquidation preference (or restrictions) of common stock that has a preference in involuntary liquidation in excess of the par or stated value of the shares (in dollars per share)						$ 0.50	$ 0.50
Convertible at the option of the holder (shares per share converted)						1
Issuance of Class A common stock (in shares)				8,000,000
Common stock, shares issued price per share (in dollars per share)				$ 29.25
Proceeds from issuance of common stock	$ 0	$ 0	$ 224,313,000	$ 224,300,000
Dividends per share	$ 0.32	$ 0.31	$ 0.30
Dividends payment covenant credit agreement based on net earnings								35,000,000
Dividends payment covenant credit agreement based on net earnings, (as a percent)								75.00%
Dividends payment covenant credit agreement based on net earnings, (Number of quarters)								4
Dividends payment covenant credit agreement based on indentures governing senior and subordinated indentures per share annually (in dollars per share)									$ 0.36
Dividends payments credit agreement bond indentures annually without consideration of coverage ratio or exhausted restricted payments baskets									20,000,000
Dividends payments credit agreement on debt in event it is in a non-payment default									$ 10,000,000