Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 7.3	$ 7.2
Accumulated depreciation	$ 284.3	$ 240.5
Preferred stock, shares authorized	15,000,000.0	15,000,000.0
Preferred stock, shares outstanding	0	0
Class A common stock
Common stock A and B, shares authorized	100,000,000.0	100,000,000.0
Common stock A and B, shares issued	22,600,000	22,000,000
Common stock A and B, shares outstanding	22,600,000	22,000,000
Class B common stock
Common stock A and B, shares authorized	25,000,000.0	25,000,000
Common stock A and B, shares issued	600,000	1,000,000
Common stock A and B, shares outstanding	600,000	1,000,000