Fair Value Measurements - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Receivables sold to Investors	$ 500,300,000	$ 500,300,000
Assets measured at fair value on a nonrecurring basis	0
Liabilities measured at fair value on a nonrecurring basis	$ 0

Amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction that continue to be recognized in the statement of financial position. Includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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