Other Assets - Restricted Investments (Details) - Restricted - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments
Expense for fair value of assets, less expenses, allocated to participants			$ 1.1	$ 1.1
Maximum
Investments
Expense period			2 years
Gain (loss) on assets	$ 0.1	$ 0.1	$ 0.1	$ 0.1