Property, Plant and Equipment

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

14. Property, Plant and Equipment

The table below sets forth the components of property, plant and equipment as of December 31, 2018 and 2017:

(in thousands)	2018		2017		Estimated useful life
Land and land improvements	$14,287		$14,853		25 years for improvements
Buildings	245,805		239,127		15 to 40 years
Machinery and equipment	989,925		950,519		5 to 15 years
Furniture and fixtures	8,091		8,861		5 years
Computer and other equipment	16,473		15,610		3 to 10 years
Software	60,182		57,847		5 to 8 years
Capital expenditures in progress	46,749		63,951
Property, plant and equipment, gross	1,381,512		1,350,768
Accumulated depreciation and amortization	(919,457	)	(896,466	)
Property, plant and equipment, net	$462,055		$454,302

Depreciation expense was $68.8 million in 2018, $61.5 million in 2017, and $58.1 million in 2016. Software amortization is recorded in Selling, general, and administrative expense and was $3.2 million in 2018, $3.6 million in 2017, and $4.0 million in 2016.

Capital expenditures, including purchased software, were $82.9 million in 2018, $87.6 million in 2017, and $73.5 million in 2016. Unamortized software cost was $6.9 million and $7.6 million as of December 31, 2018 and 2017, respectively. Expenditures for maintenance and repairs are charged to income as incurred and amounted to $19.4 million in 2018, $19.1 million in 2017, and $16.6 million in 2016.

Included in Buildings in the above table is the capitalized value of our primary manufacturing facility in Salt Lake City, Utah, which is accounted for as a build-to-suit lease with a failed sale-leaseback. As described in Note 3, during 2018 AEC finalized a modification to the lease, which includes additional manufacturing space, extends the minimum lease period until December 31, 2029 and resulted in an increase of $12.7 million to Property, plant and equipment, net (see discussion of Finance obligation in Note 17).