Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 409,075	$ 394,308
Accumulated depreciation and amortization	(281,919)	(266,357)
Property, plant and equipment, net	127,156	127,951
Depreciation and amortization	39,915	38,881	$ 36,294
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	138,592	133,455
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	55,648	54,165
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,195	21,513
Computer hardware/software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	95,716	87,416
Land, buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	92,145	90,215
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 6,779	$ 7,544