Stockholders' Equity and Earnings Per Share (Textual) (Details) $ in Millions	12 Months Ended	49 Months Ended
	Dec. 31, 2017 vote shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 shares
Class A Common Stock
Class of Stock [Line Items]
Votes per share | vote	1
Common stock, shares authorized	25,000,000	25,000,000
Treasury stock (in shares)	2,937,644	2,937,644	3,007,334
Class A Common Stock | 2016 Stock Repurchase Program
Class of Stock [Line Items]
Treasury stock, shares acquired (in shares)		1,855,923
Treasury stock, value | $		$ 101.7
Class B Common Stock
Class of Stock [Line Items]
Votes per share | vote	10
Common stock, shares authorized	6,756,176	6,756,176