Summary of Significant Accounting Policies - Impairment and Intangibles (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)
Goodwill and other intangible assets
Number of Reporting Units | item	3
Goodwill	$ 241,006,000	$ 241,006,000
Goodwill impairment	0	0
Impairment of long-lived assets	0	0
Intangible assets	275,675,000	275,675,000
Gross intangible assets	198,075,000	198,075,000
Accumulated amortization	111,953,000	100,997,000
Dealer network
Goodwill and other intangible assets
Gross intangible assets	80,000,000	80,000,000
Accumulated amortization	$ 63,000,000	59,000,000
Dealer network | Minimum
Goodwill and other intangible assets
Amortization period	15 years
Dealer 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	$ 3,713,000	3,619,000
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	$ 13,229,000	11,974,000
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
Gross intangible assets	$ 80,920,000	80,920,000
Accumulated amortization	$ 21,914,000	16,607,000
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
Gross intangible assets	$ 8,640,000	8,640,000
Accumulated amortization	$ 8,177,000	7,877,000
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	$ 113,132,000	113,132,000
Gross intangible assets	177,785,000	177,785,000
Accumulated amortization	87,964,000	82,456,000
Work Truck Solutions
Goodwill and other intangible assets
Goodwill	127,874,000
Gross intangible assets	97,890,000	97,890,000
Accumulated amortization	$ 23,989,000	$ 18,541,000