Stockholder's Equity (Stock Repurchase Program) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	May 10, 2016	Oct. 31, 2015
2013 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount						$ 60,000,000
Common Class A | 2016 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount					$ 50,000,000
Repurchased shares (in shares)	70,495	170,960	70,495	292,723
Repurchased shares, purchase price	$ 3,800,000	$ 9,100,000	$ 3,800,000	$ 16,000,000
Repurchased shares, weighted average purchase price (in USD per share)	$ 54.28	$ 53.22	$ 54.28	$ 54.69