16.	Retirement Benefit Plans

Defined Contribution Plans

We maintain various defined contribution plans, which include profit sharing and provide retirement benefits for substantially all of our employees. Matching obligations, in connection with the plans which are funded in cash and typically contributed to the plans in March of the following year, are as follows (in thousands):

	U.S. Defined Contribution
Year ended December 31,
2018	$	8,928
2017		9,153
2016		8,625

We maintain a defined contribution Supplemental Executive Retirement Plan for key employees. Under the plan, these employees may elect to defer a portion of their compensation and, in addition, we may at our discretion make contributions to the plan on behalf of the employees. In March 2017, contributions of $0.3 million were made related to calendar year 2016. In March 2018, contributions of $0.6 million were made related to calendar year 2017. We have recorded an obligation of $0.4 million for 2018.

We also have an Employee Stock Ownership Plan and Trust (“ESOP”) for employees who are not covered by a collective bargaining agreement. In connection therewith, we maintain an employee benefits trust to which we contribute shares of treasury stock. We are authorized to instruct the trustees to distribute such shares toward the satisfaction of our future obligations under the plan. The shares held in trust are not considered outstanding for purposes of calculating earnings per share until they are committed to be released. The trustees will vote the shares in accordance with its fiduciary duties. During 2018, we contributed to the trust an additional 53,300 shares from our treasury and released 53,300 shares from the trust leaving 200 shares remaining in the trust as of December 31, 2018. The provision for expense in connection with the ESOP was approximately $2.6 million in 2018, $2.2 million in 2017 and $2 million in 2016.

Defined Benefit Pension Plan

We maintain a defined benefit unfunded Supplemental Executive Retirement Plan (“SERP”). The SERP, as amended, is a defined benefit plan pursuant to which we will pay supplemental pension benefits to certain key employees upon the attainment of a contractual participant’s payment date based upon the employees’ years of service and compensation. There was no benefit obligation outstanding related to the SERP as of December 31, 2018 and 2017.

We recorded no expense related to the plan during the years ended December 31, 2018, December 31, 2017 and December 31, 2016.