Fair Values of Financial Instruments and Interest Rate Risk - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Short term borrowings due period	1 year
Current fair value of off-balance sheet financial instruments	$ 0

The face amount of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

No definition available.

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