Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Allowance for doubtful accounts	$ 6.8	$ 7.3
Accumulated depreciation	$ 298.6	$ 284.3
Preferred stock, par value (in dollars per share)	$ 0	$ 0
Preferred stock, shares authorized (in shares)	15,000,000	15,000,000
Preferred stock, shares outstanding (in shares)	0	0
Class A common stock
Common stock A and B, par value (in dollars per share)	$ 0	$ 0
Common stock A and B, shares authorized (in shares)	100,000,000	100,000,000
Common stock A and B, shares issued (in shares)	22,200,000	22,600,000
Common stock A and B, shares outstanding (in shares)	22,200,000	22,600,000
Class B common stock
Common stock A and B, par value (in dollars per share)	$ 0	$ 0
Common stock A and B, shares authorized (in shares)	25,000,000	25,000,000
Common stock A and B, shares issued (in shares)	600,000	600,000
Common stock A and B, shares outstanding (in shares)	600,000	600,000