Fixed Assets (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	$ 1,145,034	$ 998,331
Accumulated depreciation	(765,990)	(683,728)
Property, plant and equipment, net	379,044	314,603
Rental property and equipment	394,627	400,913
Accumulated depreciation	(208,886)	(212,859)
Rental property and equipment, net	185,741	188,054
Depreciation expense	149,000	140,000	$ 136,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,333	9,908
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	207,024	185,431
Capitalized software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	224,753	192,395
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 703,924	$ 610,597