Derivatives (Outstanding Interest Rate Derivatives) (Details) - Long-term $ in Millions	Jun. 30, 2019 USD ($)
Not Accounted for as Hedge | Collar
Derivative [Line Items]
Initial notional amount	$ 23.0
Interest rate	1.90%
Not Accounted for as Hedge | Swap 3.5% to 4.8%
Derivative [Line Items]
Initial notional amount	$ 40.0
Not Accounted for as Hedge | Swap 3.5% to 4.8% | Minimum
Derivative [Line Items]
Interest rate	3.50%
Not Accounted for as Hedge | Swap 3.5% to 4.8% | Maximum
Derivative [Line Items]
Interest rate	4.80%
Accounted for as Hedge | Swap 1.2%
Derivative [Line Items]
Initial notional amount	$ 50.0
Interest rate	1.20%
Accounted for as Hedge | Swap 1.8%
Derivative [Line Items]
Initial notional amount	$ 20.0
Interest rate	1.80%
Accounted for as Hedge | Swap 2.6%
Derivative [Line Items]
Initial notional amount	$ 10.0
Interest rate	2.60%
Accounted for as Hedge | Swap 2.7%
Derivative [Line Items]
Initial notional amount	$ 20.0
Interest rate	2.70%
Accounted for as Hedge | Swap 2.6%
Derivative [Line Items]
Initial notional amount	$ 40.0
Interest rate	2.60%
Accounted for as Hedge | Swap 2.5%
Derivative [Line Items]
Initial notional amount	$ 25.0
Interest rate	2.50%
Accounted for as Hedge | Swap 2.5%
Derivative [Line Items]
Initial notional amount	$ 50.0
Interest rate	2.50%
Accounted for as Hedge | Swap 2.5%
Derivative [Line Items]
Initial notional amount	$ 100.0
Interest rate	2.50%
Accounted for as Hedge | Swap 2.5%
Derivative [Line Items]
Initial notional amount	$ 50.0
Interest rate	2.50%
Accounted for as Hedge | Swap 2.5%
Derivative [Line Items]
Initial notional amount	$ 50.0
Interest rate	2.50%