Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

The following table shows estimated useful lives of property, plant and equipment:

Property, plant and equipment	Useful Life
Buildings	40 to 50 years
Leasehold improvements	Lesser of lease term or the life of the asset
Machinery, equipment and furniture	3 to 10 years
Computer software	5 to 10 years

The components of net property, plant and equipment were as follows:

	December 31,
(in millions of dollars)	2017			2016
Land and improvements	$	28.0		$	18.9
Buildings and improvements to leaseholds	152.6			119.1
Machinery and equipment	453.5			382.0
Construction in progress	11.1			8.0
	645.2			528.0
Less: accumulated depreciation	(366.7		)	(329.6		)
Property, plant and equipment, net(1)	$	278.5		$	198.4

(1) Net property, plant and equipment as of December 31, 2017 and 2016 contained $42.1 million and $34.7 million of computer software assets, respectively, which are classified within machinery and equipment and construction in progress. Amortization expense for software was $7.1 million, $7.0 million and $6.1 million for the years ended December 31, 2017, 2016 and 2015, respectively.