Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 6.2	$ 5.9
Common stock stated value per share (USD per share)	$ 20.00	$ 20.00
Authorized	50,000,000	50,000,000
Issued to voting trustees	18,665,064	17,754,923
Issued to shareholders	3,872,159	3,744,318
In treasury, at cost	(62,700)	(58,172)
Outstanding Common Stock	22,474,523	21,441,069
Common shares subscribed	997,275	958,439
Less subscripton receivable	(997,275)	(958,439)