Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Impairment and Intangibles (Details)

v3.8.0.1
Summary of Significant Accounting Policies - Impairment and Intangibles (Details)
 12 Months Ended
Dec. 31, 2017
USD ($)
item
Dec. 31, 2016
USD ($)
Dec. 31, 2015
May 01, 2017
USD ($)
Goodwill and other intangible assets        
Number of Reporting Units | item 3      
Goodwill $ 241,006,000 $ 238,286,000   $ 2,720,000
Goodwill impairment 0 0    
Finite-lived intangible asset impairment 0 0    
Impairment of long-lived assets 0 0    
Intangible assets 275,675,000 272,975,000    
Gross intangible assets 198,075,000 195,375,000    
Accumulated amortization 89,525,000 78,124,000    
Distribution network        
Goodwill and other intangible assets        
Gross intangible assets 80,000,000 80,000,000    
Accumulated amortization $ 55,000,000 51,000,000    
Distribution network | Minimum        
Goodwill and other intangible assets        
Amortization period 15 years      
Distribution network | Maximum        
Goodwill and other intangible assets        
Amortization period 20 years      
Trademark        
Goodwill and other intangible assets        
Gross intangible assets $ 5,459,000 5,459,000    
Accumulated amortization $ 3,525,000 3,431,000    
Trademark | Minimum        
Goodwill and other intangible assets        
Amortization period 7 years      
Trademark | Maximum        
Goodwill and other intangible assets        
Amortization period 25 years      
Patents        
Goodwill and other intangible assets        
Gross intangible assets $ 21,136,000 21,136,000    
Accumulated amortization $ 10,721,000 9,466,000    
Patents | Minimum        
Goodwill and other intangible assets        
Amortization period 7 years      
Patents | Maximum        
Goodwill and other intangible assets        
Amortization period 20 years      
Customer relations        
Goodwill and other intangible assets        
Amortization period     15 years  
Gross intangible assets $ 80,920,000 78,220,000    
Accumulated amortization $ 11,304,000 6,075,000    
Customer relations | Minimum        
Goodwill and other intangible assets        
Amortization period 15 years      
Customer relations | Maximum        
Goodwill and other intangible assets        
Amortization period 19 years 6 months      
Noncompete agreements        
Goodwill and other intangible assets        
Amortization period     4 years  
Gross intangible assets $ 8,640,000 8,640,000    
Accumulated amortization $ 7,055,000 6,232,000    
Noncompete agreements | Minimum        
Goodwill and other intangible assets        
Amortization period 4 years      
Noncompete agreements | Maximum        
Goodwill and other intangible assets        
Amortization period 5 years      
Work Truck Attachments segment        
Goodwill and other intangible assets        
Goodwill $ 160,932,000 160,932,000    
Gross intangible assets 195,175,000 195,175,000    
Accumulated amortization 81,336,000 74,432,000    
Work Truck Solutions segment        
Goodwill and other intangible assets        
Goodwill 80,074,000 77,354,000    
Gross intangible assets 80,500,000 77,800,000    
Accumulated amortization $ 8,189,000 $ 3,692,000