Consolidated Balance Sheets (Parenthetical) $ in Millions	Mar. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Trade accounts receivable, allowance for doubtful accounts (in dollars) | $	$ 15.3	$ 15.0
Preferred Stock, par value (in dollars per share) | $ / shares	$ 0.10	$ 0.10
Preferred Stock, shares authorized	5,000,000	5,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Class A
Common Stock, par value (in dollars per share) | $ / shares	$ 0.10	$ 0.10
Common Stock, shares authorized	80,000,000	80,000,000
Common Stock, votes per share (Number of votes)	1	1
Common Stock, issued shares	27,710,297	27,646,465
Common Stock, outstanding shares	27,710,297	27,646,465
Class B
Common Stock, par value (in dollars per share) | $ / shares	$ 0.10	$ 0.10
Common Stock, shares authorized	25,000,000	25,000,000
Common Stock, votes per share (Number of votes)	10	10
Common Stock, issued shares	6,279,290	6,329,290
Common Stock, outstanding shares	6,279,290	6,329,290