Note 2. Revenue from Contracts with Customers

The Company’s revenues are primarily derived from the sale of products in product lines within our Performance Materials, Specialty Minerals, Refractories and Energy Services businesses. Our primary performance obligation (the sale of products) is satisfied upon shipment or delivery to our customers based on written sales terms, which is also when control is transferred. In most of our contracts in our Paper PCC product line, which is in our Specialty Minerals segment, the price per ton is based upon the total number of tons sold to the customer during the year. Under these contracts, the price billed to the customer for shipments during the year is based on periodic estimates of the total annual volume that will be sold to such customer. Revenues are adjusted at the end of each year to reflect the actual volume sold. The Company also has consignment arrangements with certain customers in our Refractories segment. Revenues for these transactions are recorded when the consigned products are consumed by the customer and control is transferred to the customer.

Revenue from sales of equipment, primarily in our Refractory products product line within our Refractories segment, is recorded upon completion of installation and control is transferred to the customer. Revenue from services is recorded when the services have been performed. Included within our Refractory products product line are certain consignment arrangements with certain customers in our Refractories segment. Revenues for these transactions are recorded when the consigned products are consumed by the customer and control is transferred.

Revenue from long-term construction, primarily in our Energy Services segment, where our performance obligations are satisfied in phases, is recognized over time using certain input measures based on the measurement of the value transferred to the customer, including milestones achieved.

The following table disaggregates our revenue by major source (product line) for the years ended December 31, 2018, 2017 and 2016:

	Year Ended December 31,
(millions of dollars)	2018		2017		2016
Net Sales
Metalcasting	$	328.9	$	294.3	$	258.0
Household, Personal Care and Specialty Products		248.8		169.6		171.2
Environmental Products		80.3		67.7		78.9
Building Materials		70.4		78.2		74.1
Basic Minerals		99.7		125.0		103.9
Performance Materials		828.1		734.8		686.1

Paper PCC		378.5		377.7		387.9
Specialty PCC		66.9		66.0		64.3
Ground Calcium Carbonate		91.0		87.3		83.6
Talc		52.9		53.8		55.7
Specialty Minerals		589.3		584.8		591.5

Refractory Products		261.1		226.9		219.0
Metallurgical Products		50.8		52.5		55.5
Refractories		311.9		279.4		274.5

Energy Services		78.3		76.7		85.9

Total	$	1,807.6	$	1,675.7	$	1,638.0