(13) Defined Benefit Plans and Other Postretirement Benefits

We sponsor several defined benefit pension plans primarily in the United States and the United Kingdom. In the U.S., we have three noncontributory defined benefit pension plans. Plan benefits in two of the plans are frozen while one plan remains active. Benefits are generally based on years of service and compensation during the span of employment. In the U.K., we assumed several defined benefit plans as part of our acquisition of Halcrow on November 10, 2011, of which the largest is the Halcrow Pension Scheme. These defined benefit plans have been closed to new entrants for many years. The information related to these plans is presented in the Non‑U.S. Pension Plans columns of the tables below.

The components of the net periodic pension expense for the three and six months ended June 24, 2016 and June 26, 2015 are detailed below:


	Three Months Ended
	June 24, 2016				June 26, 2015
	U.S.		Non-U.S.		U.S.		Non-U.S.
($ in thousands)	Pension Plans		Pension Plans		Pension Plans		Pension Plans
Service cost	$	671	$	1,378	$	863	$	880
Interest cost		2,954		10,487		2,810		10,905
Expected return on plan assets		(2,921)		(8,822)		(3,312)		(7,848)
Amortization of prior service credits		(188)		—		(191)		—
Recognized net actuarial loss		1,629		693		1,865		983
Net expense included in current income	$	2,145	$	3,736	$	2,035	$	4,920


	Six Months Ended
	June 24, 2016				June 26, 2015
	U.S.		Non-U.S.		U.S.		Non-U.S.
($ in thousands)	Pension Plans		Pension Plans		Pension Plans		Pension Plans
Service cost	$	1,342	$	2,755	$	1,725	$	1,759
Interest cost		5,908		20,964		5,620		21,799
Expected return on plan assets		(5,842)		(17,636)		(6,624)		(15,687)
Amortization of prior service credits		(376)		—		(383)		—
Recognized net actuarial loss		3,258		1,386		3,733		1,965
Net expense included in current income	$	4,290	$	7,469	$	4,071	$	9,836

We sponsor a medical benefit plan for retired employees of certain subsidiaries. The plan is contributory, and retiree premiums are based on years of service at retirement. The benefits contain limitations and a cap on future cost increases. We fund postretirement medical benefits on a pay‑as‑you‑go basis. Additionally, we have a frozen non‑qualified pension plan that provides additional retirement benefits to certain senior executives who remained employed and retired from CH2M on or after age 65.

The components of the non-qualified pension benefit expense and postretirement benefit expense for the three and six months ended June 24, 2016 and June 26, 2015 are detailed below:


	Three Months Ended
	June 24, 2016				June 26, 2015
	Non-Qualified		Postretirement		Non-Qualified		Postretirement
($ in thousands)	Pension Plan		Benefit Plans		Pension Plan		Benefit Plans
Service cost	$	—	$	206	$	—	$	242
Interest cost		13		497		15		524
Amortization of prior service (credits) costs		—		(96)		—		(7)
Recognized net actuarial loss (gain)		—		(3)		—		(2)
Net expense included in current income	$	13	$	604	$	15	$	757


	Six Months Ended
	June 24, 2016				June 26, 2015
	Non-Qualified		Postretirement		Non-Qualified		Postretirement
($ in thousands)	Pension Plan		Benefit Plans		Pension Plan		Benefit Plans
Service cost	$	—	$	413	$	—	$	483
Interest cost		27		994		29		1,049
Amortization of prior service (credits) costs		—		(192)		—		(15)
Recognized net actuarial loss (gain)		—		(6)		1		(3)
Net expense included in current income	$	27	$	1,209	$	30	$	1,514