Segment Reporting and Geographic Locations - Sales by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Revenues	$ 188,339	$ 198,349	$ 195,127	$ 173,416	$ 149,966	$ 153,604	$ 178,251	$ 180,291	$ 755,231	$ 662,112	$ 825,341
Gross Profit	23,211	25,150	22,701	21,503	18,276	18,919	24,331	25,704	92,565	87,230	110,822
Depreciation and Amortization Expense									15,344	16,451	17,710
Selling, General & Administrative Expenses									59,800	60,542	71,469
Operating Income	$ 8,638	$ 10,682	$ 7,568	$ 4,557	$ 3,910	$ 4,466	$ 8,427	$ 8,580	31,445	25,383	38,026
Capital Expenditures and Other Items:
Capital Expenditures									13,567	11,917	15,590
Other Items									4,300	4,123	2,332
Global Truck & Bus
Revenues
Revenues									457,770	416,279	565,269
Global Construction & Agriculture
Revenues
Revenues									309,707	254,024	271,627
Operating Segments
Revenues
Revenues									755,231	662,112	825,341
Operating Segments | Global Truck & Bus
Revenues
Revenues									455,864	415,154	564,651
Gross Profit									62,668	54,665	85,702
Depreciation and Amortization Expense									7,875	8,545	8,909
Selling, General & Administrative Expenses									21,507	22,557	25,263
Operating Income									39,983	30,943	59,252
Capital Expenditures and Other Items:
Capital Expenditures									6,290	6,384	7,579
Other Items									777	2,712	1,838
Operating Segments | Global Construction & Agriculture
Revenues
Revenues									299,367	246,958	260,690
Gross Profit									31,291	34,060	28,627
Depreciation and Amortization Expense									4,736	5,581	5,855
Selling, General & Administrative Expenses									16,845	18,240	20,442
Operating Income									14,305	15,680	8,044
Capital Expenditures and Other Items:
Capital Expenditures									5,324	4,609	4,688
Other Items									1,146	723	494
Intersegment Revenues | Global Truck & Bus
Revenues
Revenues									1,906	1,125	618
Intersegment Revenues | Global Construction & Agriculture
Revenues
Revenues									10,340	7,066	10,937
Corporate/ Other
Revenues
Revenues									(12,246)	(8,191)	(11,555)
Gross Profit									(1,394)	(1,495)	(3,507)
Depreciation and Amortization Expense									2,733	2,325	2,946
Selling, General & Administrative Expenses									21,448	19,745	25,764
Operating Income									(22,843)	(21,240)	(29,270)
Capital Expenditures and Other Items:
Capital Expenditures									1,953	924	3,323
Other Items									$ 2,377	$ 688	$ 0