National Holdings Corporation - Amortization is calculated using the straight-line method over the estimated useful lives (Detail)
|12 Months Ended|
Dec. 31, 2017
|Acquired Finite-lived Intangible Assets, Weighted Average Useful Life||10 years|
|Customer Lists [Member]|
|Acquired Finite-lived Intangible Assets, Weighted Average Useful Life||6 years|
Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
Reference 1: http://www.xbrl.org/2003/role/presentationRef