Pension plans and other postretirement benefits (Tables)

9 Months Ended

Sep. 30, 2015

Compensation and Retirement Disclosure [Abstract]

Net Periodic Pension Expense 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 September 30
	2015			2014			2015			2014
	(in thousands)
Service cost	$	5,916			5,130			188			151
Interest cost on projected benefit obligation		17,754			17,290			651			695
Expected return on plan assets		(23,527	)		(22,892	)		—			—
Amortization of prior service credit		(1,501	)		(1,638	)		(340	)		(340	)
Amortization of net actuarial loss		11,207			3,624			26			—
Net periodic benefit cost	$	9,849			1,514			525			506
	Pension benefits						Other postretirement benefits
	Nine months ended September 30
	2015			2014			2015			2014
	(in thousands)
Service cost	$	17,748			15,390			562			453
Interest cost on projected benefit obligation		53,261			51,871			1,953			2,084
Expected return on plan assets		(70,578	)		(68,676	)		—			—
Amortization of prior service credit		(4,504	)		(4,914	)		(1,019	)		(1,019	)
Amortization of net actuarial loss		33,619			10,871			79			—
Net periodic benefit cost	$	29,546			4,542			1,575			1,518