Retirement Benefit Plans

3 Months Ended

Sep. 30, 2017

8. Retirement Benefit Plans

We sponsor various retirement benefit plans including qualified and nonqualified defined benefit pension plans for our employees. The components of net periodic pension expense are as follows (in thousands):

	Three Months Ended September 30,
	2016		2017
Service cost	$	224	$	216
Interest cost	7		8
Amortization of prior service cost	70		70

Net periodic pension expense	$	301	$	294

For the three months ended September 30, 2016, we made no contributions to these defined benefit plans. For the three months ended September 30, 2017, we made contributions of $0.7 million to these defined benefit plans.

In addition, we maintain various defined contribution plans. For the three months ended September 30, 2016 and 2017, we made contributions of $1.2 and $1.6 million, respectively, to these defined contribution plans.