Derivatives (Fair Value of Derivative Instruments) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liability	$ 3.0
Derivative, Maturity Date	May 23, 2023
Derivative, notional amount	$ 1,047.3
Derivative, Fair Value, Net	$ 7.0	$ 9.7
Derivative, Fixed Interest Rate	1.83%
Derivative Asset, Fair Value, Gross Liability	$ 3.2
Interest Rate Swaps 2019 Maturity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	250.0
Derivative, Fair Value, Net	$ 0.0	0.8
Derivative, Fixed Interest Rate	1.43947%
Interest Rate Swaps 2020 Maturity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	$ 100.0
Derivative, Fair Value, Net	$ 1.9	1.9
Derivative, Fixed Interest Rate	1.2337%
Interest Rate Swaps 2021 Maturity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	$ 397.3
Derivative, Fair Value, Net	$ 8.1	$ 7.0
Derivative, Fixed Interest Rate	1.57113%
Interest Rate Swaps 2023 Maturity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	$ 50.0
Derivative, Fair Value, Net	$ (0.4)
Derivative, Fixed Interest Rate	2.62%
Interest Rate Forward Starting Swaps 2023 Maturity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, notional amount	$ 250.0
Derivative, Fair Value, Net	$ (2.6)
Derivative, Fixed Interest Rate	2.71%