Fair Value Measurements - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($)
Fair Value Disclosures [Abstract]
Financial instruments transferred into or out of Level 3 classification	$ 0

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

No definition available.

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration