Related party transactions

The significant related party transactions occurring during the years ended December 31, 2017, 2016 and 2015 are described below. We believe all of our transactions with Glencore and BHH were at prices that approximate market.

Glencore ownership

As of December 31, 2017, Glencore plc and its affiliates (together "Glencore") beneficially owned 42.9% of Century’s outstanding common stock (47.4% on a fully-diluted basis assuming the conversion of all of the Series A Convertible Preferred Stock) and all of our outstanding Series A Convertible Preferred stock. See Note 6. Shareholders' equity for a full description of our outstanding Series A Convertible Preferred stock. From time to time Century and Glencore enter into various transactions for the purchase and sale of primary aluminum, purchase and sale of alumina, tolling agreements and certain forward financial contracts.

Sales to Glencore

For the year ended December 31, 2017, we derived approximately 75% of our consolidated sales from Glencore. Glencore purchases the aluminum we produce for resale.

Glencore purchased substantially all of the aluminum produced at our North American smelters in 2015 and 2016 and purchased certain aluminum products produced at our North American smelters in 2017. Glencore purchased substantially all of the primary aluminum produced at Grundartangi in 2015, 2016 and 2017. We have entered into agreements with Glencore pursuant to which Glencore has agreed to purchase aluminum produced from our U.S. and Icelandic operations through 2018 and 2019, respectively. Glencore purchases aluminum produced at our North American smelters at prices based on the LME plus the Midwest regional delivery premium and any additional negotiated product premiums. Glencore purchases aluminum produced at our Grundartangi, Iceland smelter at prices based on the LME plus the European Duty Paid premium and any applicable product premiums.

We received tolling fees from Glencore under a tolling agreement that provided for delivery of primary aluminum produced at Grundartangi through June 2016. The fee paid by Glencore under this tolling agreement was based on the LME price for primary aluminum plus a portion of the European Duty Paid premium.

Purchases from Glencore

We purchase a portion of our alumina requirements from Glencore under a long-term supply agreement and on a spot basis at prices based on a published alumina index.

Financial contracts with Glencore

During 2017, we entered into certain financial contracts with Glencore. See Note 19. Derivatives regarding these forward financial sales contracts.

Transactions with BHH

We own a 40% stake in BHH and had an agreement to purchase carbon anodes from them for use in our manufacturing operations through 2017. In the fourth quarter of 2015, we completed the construction of a second furnace at our carbon anode facility in Vlissingen, Netherlands. This investment increased our capacity to produce carbon anodes and reduced our need to source carbon anodes from BHH. As a result, in the fourth quarter of 2015, we made the decision to pursue an exit from our investment in BHH. In connection with our exit plan, we concluded that our investment in BHH was other than temporarily impaired and recorded a charge of $11,584. Fair value for the investment was based on a proposed sale transaction for a portion of the investment.

Summary

A summary of the aforementioned significant related party transactions for the years ended December 31, 2017, 2016 and 2015 is as follows:



	Year Ended December 31,
	2017		2016		2015
Net sales to Glencore	$	1,198,076	$	1,178,631	$	1,867,711
Purchases from Glencore	253,044		231,850		393,158
Purchases from BHH	15,763		10,127		46,592