Executive Retirement (Detail) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($)
Restructuring and Related Activities [Abstract]
Separation Agreement, Consulting Fees	$ 0.3
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost	$ 0.6

Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

No definition available.

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