Pension plans and other postretirement benefits (Tables)

6 Months Ended

Jun. 30, 2016

Compensation and Retirement Disclosure [Abstract]

Net Periodic Defined Benefit Cost for Defined Benefit Plans

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

	Pension benefits						Other postretirement benefits
	Three months ended June 30
	2016			2015			2016			2015
	(in thousands)
Service cost	$	6,137			5,832			340			174
Interest cost on projected benefit obligation		20,822			17,732			1,281			652
Expected return on plan assets		(26,423	)		(23,476	)		—			—
Amortization of prior service credit		(789	)		(1,478	)		(330	)		(329	)
Amortization of net actuarial loss		6,773			11,237			30			28
Net periodic benefit cost	$	6,520			9,847			1,321			525
	Pension benefits						Other postretirement benefits
	Six months ended June 30
	2016			2015			2016			2015
	(in thousands)
Service cost	$	12,519			11,832			798			374
Interest cost on projected benefit obligation		41,705			35,507			2,486			1,302
Expected return on plan assets		(54,237	)		(47,051	)		—			—
Amortization of prior service credit		(1,614	)		(3,003	)		(680	)		(679	)
Amortization of net actuarial loss		15,073			22,412			30			53
Net periodic benefit cost	$	13,446			19,697			2,634			1,050