Annual report pursuant to Section 13 and 15(d)

Property and Equipment - Schedule Of National’s property and equipment (Detail)

v3.8.0.1
Property and Equipment - Schedule Of National’s property and equipment (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Sep. 30, 2016
Property, Plant and Equipment [Line Items]        
Property Plant And Equipment Gross   $ 2,872   $ 1,200
Less: Accumulated depreciation   (475)   (36)
Property Plant And Equipment Net $ 9,513 2,397 $ 7,376 1,164
Equipment [Member]        
Property, Plant and Equipment [Line Items]        
Property Plant And Equipment Gross   1,306   600
Property Plant And Equipment Useful Life 5 years      
Furniture And Fixtures [Member]        
Property, Plant and Equipment [Line Items]        
Property Plant And Equipment Gross   284   65
Property Plant And Equipment Useful Life 5 years      
Leaseholds And Leasehold Improvements [Member]        
Property, Plant and Equipment [Line Items]        
Property Plant And Equipment Gross   1,006   259
Property, Plant and Equipment, Estimated Useful Lives Lesser of useful life or term of lease      
Assets Held under Capital Leases [Member]        
Property, Plant and Equipment [Line Items]        
Property Plant And Equipment Gross   $ 276   $ 276
Property Plant And Equipment Useful Life 5 years