RETIREMENT PLANS

Our subsidiaries participate in a qualified 401(k) defined contribution plan under which employees may contribute a percentage of their salary. Employees are eligible to participate upon their first day of employment. Under this plan, we match 100% of the first 6% that the employee defers. During the second quarter of 2018, we made a one-time discretionary contribution of $0.9 million to the vast majority of our employees following the tax reform that was enacted in December 2017. Additionally, we may provide a performance-based company contribution of up to 3% if we exceed annual financial goals. Our contribution expense is presented in the following table:



	Six Months Ended June 30,
(in thousands)	2018		2017
401(k) contribution expense	$	8,146	$	6,150

We also sponsor an Employee Retirement Income Security Act of 1974 (ERISA) Excess Lost Match Plan for certain officers. This plan provides retirement benefits equal to the difference, if any, between the maximum benefit allowable under the Internal Revenue Code and the amount that would have been provided under the qualified 401(k) defined contribution plan, if no limits were applied.

Additionally, we sponsor a qualified non-contributory defined benefit pension plan and two supplemental non-qualified retirement plans that have been frozen. The net periodic benefit credit for these plans includes the following components:



	Three Months Ended June 30,						Six Months Ended June 30,
(in thousands)	2018			2017			2018			2017
Service cost	$	(4	)	$	(4	)	$	(8	)	$	(8	)
Interest cost	1,560			1,477			3,120			2,954
Expected return on plan assets	(2,895		)	(2,427		)	(5,790		)	(4,854		)
Amortization:
Unrecognized prior service cost	—			2			—			4
Unrecognized loss	623			628			1,246			1,256
Net periodic pension credit	$	(716	)	$	(324	)	$	(1,432	)	$	(648	)