Fixed Assets (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	$ 1,209,361	$ 1,129,564
Accumulated depreciation	(799,247)	(756,061)
Property, plant and equipment, net	410,114	373,503
Rental property and equipment	371,908	386,039
Accumulated depreciation	(193,809)	(202,083)
Rental property and equipment, net	178,099	183,956
Depreciation expense	159,000	146,000	$ 134,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,333	9,333
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	198,025	206,752
Capitalized software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	283,446	224,754
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 718,557	$ 688,725