On March 18, 2010, the Compensation Committee and the Board of Directors of the Company approved and adopted the Universal Display Corporation Supplemental Executive Retirement Plan (SERP), effective as of April 1, 2010. On March 3, 2015, the Compensation Committee and the Board of Directors amended the SERP to include salary and bonus as part of the plan. Prior to this amendment, the SERP benefit did not take into account any bonuses. This change increased the liability for certain participants in the SERP. The purpose of the SERP, which is unfunded, is to provide certain of the Company’s key employees with supplemental retirement benefits following a cessation of their employment and to encourage their continued employment with the Company. As of September 30, 2019, there were seven participants in the SERP.

The Company records amounts relating to the SERP based on calculations that incorporate various actuarial and other assumptions, including discount rates, rate of compensation increases, retirement dates and life expectancies. The net periodic costs are recognized as employees render the services necessary to earn the SERP benefits.

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Service cost	$	227	$	326	$	742	$	976
Interest cost		403		261		1,209		785
Amortization of prior service cost		399		420		1,197		1,262
Amortization of loss		410		119		1,231		355
Total net periodic benefit cost	$	1,439	$	1,126	$	4,379	$	3,378