Consolidated Balance Sheets Parenthetical - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5.9	$ 6.0
Common stock stated value per share (USD per share)	$ 20	$ 20
Authorized	50,000,000	50,000,000
Issued to voting trustees	17,754,923	15,912,467
Issued to shareholders	3,744,318	3,496,114
In treasury, at cost	(58,172)	(24,243)
Outstanding Common Stock	21,441,069	19,384,338
Common Stock, Shares Subscribed	958,439	923,156
Subscripton Receivable	(958,439)	(923,156)