Other Assets - Restricted Investments (Details) - Restricted - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 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

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

No definition available.

Name:	us-gaap_DebtSecuritiesRealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration