Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 440,994	$ 409,075
Accumulated depreciation and amortization	(306,643)	(281,919)
Property, plant and equipment, net	134,351	127,156
Depreciation and amortization	38,472	39,915	$ 38,881
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	151,339	138,592
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	58,205	55,648
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,655	20,195
Computer hardware/software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	98,415	95,716
Land, buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	97,937	92,145
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 14,443	$ 6,779