Property, Plant, and Equipment

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment [Abstract]

Property, plant, and equipment on the Consolidated Balance Sheets is summarized as follows:


	December 31,
(Thousands)	2021		2020
Land	$	26,627	$	5,686
Buildings	173,907		165,144
Machinery and equipment	687,502		645,195
Software	45,445		43,652
Construction in progress	130,838		69,297
Allowances for depreciation	(690,166)		(662,724)
Subtotal	374,153		266,250
Finance leases	32,865		34,301
Allowances for depreciation	(6,193)		(4,914)
Subtotal	26,672		29,387
Mineral resources	4,980		4,979
Mine development	30,059		30,058
Allowances for amortization and depletion	(26,889)		(20,988)
Subtotal	8,150		14,049
Property, plant, and equipment — net	$	408,975	$	309,686

The Company received $63.5 million from the U.S. Department of Defense (DoD), in previous periods, for reimbursement of the DoD's share of the cost of equipment. This amount was recorded in property, plant, and equipment and the reimbursements are reflected in Unearned income on the Consolidated Balance Sheets. The equipment was placed in service during 2012, and its full cost is being depreciated in accordance with Company policy. The unearned income liability is being reduced ratably with the depreciation expense recorded over the life of the equipment. Unearned income was reduced by $4.3 million in both 2021 and 2020 and $4.4 million in 2019 and credited to cost of sales in the Consolidated Statements of Income, offsetting the impact of the depreciation expense on the associated equipment on the Company's cost of sales and gross margin.

We recorded depreciation and depletion expense of $31.4 million in 2021, $30.9 million in 2020, and $30.3 million in 2019. Depreciation, depletion, and amortization as shown on the Consolidated Statement of Cash Flows is net of the reduction in the unearned income liability in 2021, 2020, and 2019. The net carrying value of capitalized software was $5.4 million and $5.0 million at December 31, 2021 and December 31, 2020, respectively. Depreciation expense related to software was $1.8 million, $1.8 million, and $2.4 million in 2021, 2020, and 2019, respectively.