Fair Value Measurements - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Deferred finance costs, net	$ 9.6	$ 11.3
Carrying Value
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Secured borrowings	517.1	522.9
Level 3 \| Estimated Fair Value
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Secured borrowings	$ 519.5	$ 527.9

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant