Fair Value - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Liabilities, recurring	$ 0	$ 0

Aggregation of the liabilities reported on the balance sheet measured at fair value on a recurring basis by the entity.

No definition available.

Name:	us-gaap_LiabilitiesFairValueDisclosureRecurring
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant