Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Condensed Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts	$ 7.0	$ 6.2
Common stock stated value per share (USD per share)	$ 20.00	$ 20.00
Authorized	50,000,000	50,000,000
Issued to voting trustees	19,064,627	18,665,064
Issued to shareholders	3,943,540	3,872,159
In treasury, at cost	(271,199)	(62,700)
Outstanding Common Stock	22,736,968	22,474,523