Pension plans and other postretirement benefits (Tables)

3 Months Ended

Mar. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Net Periodic Pension Expense for Defined Benefit Plans

Net periodic pension expense for defined benefit plans consisted of the following:

	Pension benefits						Other postretirement benefits
	Three months ended March 31
	2016			2015			2016			2015
	(in thousands)
Service cost	$	6,382			6,000			458			200
Interest cost on projected benefit obligation		20,883			17,775			1,205			650
Expected return on plan assets		(27,814	)		(23,575	)		—			—
Amortization of prior service credit		(825	)		(1,525	)		(350	)		(350	)
Amortization of net actuarial loss		8,300			11,175			—			25
Net periodic benefit cost	$	6,926			9,850			1,313			525