Stockholders Equity (Narrative) (Details) - 2013 Stock Repurchase Program - Shares Outstanding Class A - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Nov. 12, 2013
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 60,000,000
Treasury stock acquisition	$ 7,200,000	$ 12,200,000	$ 23,200,000	$ 26,400,000
Stock repurchase program, shares acquired during period	134,186	235,194	426,909	501,531
Stock repurchase program, shares acquired during period, weighted-average cost per share	$ 53.95	$ 51.86	$ 54.46	$ 52.73