Derivatives (Interest Rate Contracts) (Details) - Not designated as hedging $ in Millions	Dec. 31, 2018 USD ($)
Long-term Interest Rate Swap 2014
Open interest rate contracts
Initial Notional Amount (in millions)	$ 23.0
Interest Rate	1.90%
Long-term Interest Rate Collar 2013
Open interest rate contracts
Initial Notional Amount (in millions)	$ 40.0
Long-term Interest Rate Collar 2013 | Minimum
Open interest rate contracts
Interest Rate	2.90%
Long-term Interest Rate Collar 2013 | Maximum
Open interest rate contracts
Interest Rate	4.80%
Long-term Interest Rate Swap 2018
Open interest rate contracts
Initial Notional Amount (in millions)	$ 40.0
Interest Rate	2.60%
Long-term Interest Rate Swap 2018
Open interest rate contracts
Initial Notional Amount (in millions)	$ 25.0
Interest Rate	2.50%