Derivatives - Fair Value of Derivative Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate Notional Value	$ 796.9
Aggregate Fair Value	$ 0.5	$ 7.0
Weighted Average Interest Rate	1.95%
Interest Rate Swaps 2020 Maturity
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate Notional Value	$ 100.0
Aggregate Fair Value	$ 1.4	1.9
Weighted Average Interest Rate	1.23%
Interest Rate Swaps 2021 Maturity
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate Notional Value	$ 396.9
Aggregate Fair Value	$ 5.1	8.1
Weighted Average Interest Rate	1.57%
Interest Rate Swaps 2022 Maturity
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate Notional Value	$ 0.0
Aggregate Fair Value	$ 0.0	0.0
Weighted Average Interest Rate	0.00%
Interest Rate Swaps 2023 Maturity
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate Notional Value	$ 200.0
Aggregate Fair Value	$ (4.1)	(2.0)
Weighted Average Interest Rate	2.67%
Interest Rate Forward Starting Swaps 2023 Maturity
Derivative Instruments, Gain (Loss) [Line Items]
Aggregate Notional Value	$ 100.0
Aggregate Fair Value	$ (1.9)	$ (1.0)
Weighted Average Interest Rate	2.75%

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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