Pension plans and other postretirement benefits (Tables)

3 Months Ended

Mar. 31, 2015

Compensation and Retirement Disclosure [Abstract]

Net Periodic Pension Expense for Defined Benefit Plans

Net periodic benefit cost for defined benefit plans consisted of the following:

	Pension benefits						Other postretirement benefits
	Three months ended March 31
	2015			2014			2015			2014
	(in thousands)
Service cost	$	6,000			5,100			200			150
Interest cost on projected benefit obligation		17,775			17,250			650			675
Expected return on plan assets		(23,575	)		(22,925	)		—			—
Amortization of prior service credit		(1,525	)		(1,650	)		(350	)		(350	)
Amortization of net actuarial loss		11,175			3,350			25			—
Net periodic benefit cost	$	9,850			1,125			525			475