Stockholders Equity (Narrative) (Details) - 2013 Stock Repurchase Program - Shares Outstanding Class A - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Nov. 12, 2013
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 60,000,000
Treasury stock acquisition	$ 9,100,000	$ 9,300,000	$ 16,000,000	$ 14,200,000
Stock repurchase program, shares acquired during period	170,960	175,359	292,723	266,337
Stock repurchase program, shares acquired during period, weighted-average cost per share	$ 53.22	$ 52.82	$ 54.69	$ 53.49