Stockholders Equity (Narrative) (Details) (2013 Stock Repurchase Program, Shares Outstanding Class A, USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Nov. 12, 2013
2013 Stock Repurchase Program | Shares Outstanding Class A
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount			$ 60,000,000
Treasury stock acquisition	$ 6,900,000	$ 5,000,000
Stock repurchase program, shares acquired during period	121,763	90,978
Stock repurchase program, shares acquired during period, weighted-average cost per share	$ 56.76	$ 54.80