Segment Reporting (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 233,391	$ 195,127	$ 449,126	$ 368,543
Gross Profit	35,884	22,701	67,005	44,204
Depreciation and Amortization Expense	3,935	3,887	7,748	7,803
Selling, General & Administrative Expenses	14,433	14,802	29,736	31,421
Operating Income	21,124	7,568	36,610	12,125
Capital and Other Expenditures [Abstract]
Capital Expenditures	3,392	3,156	5,158	7,843
Other Items		877		4,328
Operating Segments
Segment Reporting Information [Line Items]
Revenues	233,391	195,127	449,126	368,543
Corporate/ Other
Segment Reporting Information [Line Items]
Revenues	(4,051)	(2,964)	(7,786)	(5,141)
Gross Profit	(377)	(329)	(762)	(685)
Depreciation and Amortization Expense	788	749	1,456	1,379
Selling, General & Administrative Expenses	4,791	5,126	10,316	11,808
Operating Income	(5,168)	(5,454)	(11,078)	(12,494)
Capital and Other Expenditures [Abstract]
Capital Expenditures	1,110	1,060	1,231	1,319
Other Items		0		2,377
Global Truck & Bus
Segment Reporting Information [Line Items]
Revenues	148,744	119,910	277,047	221,998
Global Truck & Bus | Operating Segments
Segment Reporting Information [Line Items]
Revenues	147,983	119,603	275,474	221,466
Gross Profit	23,219	17,070	42,189	31,107
Depreciation and Amortization Expense	1,898	1,949	3,757	4,012
Selling, General & Administrative Expenses	5,710	5,701	11,222	11,154
Operating Income	17,217	11,073	30,379	19,366
Capital and Other Expenditures [Abstract]
Capital Expenditures	1,011	836	1,849	4,048
Other Items		3		968
Global Truck & Bus | Intersegment Revenues
Segment Reporting Information [Line Items]
Revenues	761	307	1,573	532
Global Construction & Agriculture
Segment Reporting Information [Line Items]
Revenues	88,698	78,181	179,865	151,686
Global Construction & Agriculture | Operating Segments
Segment Reporting Information [Line Items]
Revenues	85,408	75,524	173,652	147,077
Gross Profit	13,042	5,960	25,578	13,782
Depreciation and Amortization Expense	1,249	1,189	2,535	2,412
Selling, General & Administrative Expenses	3,932	3,975	8,198	8,459
Operating Income	9,075	1,949	17,309	5,253
Capital and Other Expenditures [Abstract]
Capital Expenditures	1,271	1,260	2,078	2,476
Other Items		874		983
Global Construction & Agriculture | Intersegment Revenues
Segment Reporting Information [Line Items]
Revenues	$ 3,290	$ 2,657	$ 6,213	$ 4,609