We have a defined benefit pension plan (pension plan) that covers certain U.S. citizen employees and other employees who are permanent residents of the United States. Benefits are based on years of service and employee compensation. The Board of Directors amended the pension plan to discontinue the accrual of benefits once the plan was frozen on December 31, 2010. We did not contribute to the pension plan during the quarters ended March 31, 2019 and 2018, and are not required to contribute to the pension plan during the remaining quarters of calendar year 2019; however, we may, at our discretion, make contributions to the plan in order to manage our plan expenses.

We also support a non-contributory, defined benefit supplemental executive retirement plan (supplemental plan) that provided pension benefits to certain employees in excess of those allowed under our tax-qualified pension plan. Effective March 4, 2010, the supplemental plan was closed to new participants. The supplemental plan is a non-qualified plan and, as such, we are not required to make contributions to the supplemental plan. We contributed an immaterial amount to the supplemental plan during the quarters ended March 31, 2019 and 2018, and do not expect contributions to the supplemental plan to be material during the remaining quarters of 2019. Our obligations under the supplemental plan were $20.5 million and $21.4 million as of March 31, 2019 and December 31, 2018, respectively and are included in “accrued costs and expenses” and “other liabilities” on the consolidated balance sheet.

We also have defined benefit pension plans that covers certain Norwegian citizen employees and other employees who are permanent residents of Norway. Benefits are based on years of service and employee compensation. We did not contribute to the Norwegian defined benefit pension plans during the quarters ended March 31, 2019 and 2018, respectively and we do not expect to make any contributions during the remainder of calendar year 2019.

The net periodic benefit cost for our defined benefit pension plans and supplemental plan (referred to collectively as “Pension Benefits”) is comprised of the following components:

	Three Months			Three Months
	Ended			Ended
(In thousands)	March 31, 2019			March 31, 2018
Pension Benefits:
Service cost	$	56			30
Interest cost		932			902
Expected return on plan assets		(563	)		(483	)
Administrative expenses		10			1
Amortization of net actuarial losses		72			—
Net periodic pension cost	$	507			450