Annual report pursuant to Section 13 and 15(d)

Business and Credit Concentrations - Company's Top Five Manufacturers Produced (Detail)

v3.8.0.1
Business and Credit Concentrations - Company's Top Five Manufacturers Produced (Detail) - Cost of Goods, Total [Member] - Supplier Concentration Risk [Member]
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Concentration Risk [Line Items]      
Percentage of total production 47.50% 51.00% 56.50%
Manufacturer One [Member]      
Concentration Risk [Line Items]      
Percentage of total production 17.90% 22.90% 31.50%
Manufacturer Two [Member]      
Concentration Risk [Line Items]      
Percentage of total production 11.10% 10.10% 9.10%
Manufacturer Three [Member]      
Concentration Risk [Line Items]      
Percentage of total production 8.80% 8.80% 7.30%
Manufacturer Four [Member]      
Concentration Risk [Line Items]      
Percentage of total production 5.40% 4.90% 5.00%
Manufacturer Five [Member]      
Concentration Risk [Line Items]      
Percentage of total production 4.30% 4.30% 3.60%