Employee benefit plans

3 Months Ended

Mar. 31, 2017

Compensation and Retirement Disclosure [Abstract]

Pension and other postretirement benefit plans

Employee benefit plans

Pension and other postretirement plans

The Company has noncontributory defined benefit pension plans and other postretirement benefit plans for certain eligible employees. Components of net periodic benefit cost for the Company's pension and other postretirement benefit plans were as follows:

	Pension Benefits						Other Postretirement Benefits
Three Months Ended March 31,	2017			2016			2017			2016
	(In thousands)
Components of net periodic benefit cost:
Service cost	$	—		$	—		$	447		$	450
Interest cost	4,014			4,390			808			949
Expected return on assets	(5,029		)	(5,280		)	(1,145		)	(1,149		)
Amortization of prior service credit	—			—			(343		)	(343		)
Amortization of net actuarial loss	1,793			1,593			336			448
Net periodic benefit cost, including amount capitalized	778			703			103			355
Less amount capitalized	107			81			(39		)	34
Net periodic benefit cost	$	671		$	622		$	142		$	321

Nonqualified benefit plans

In addition to the qualified plan defined pension benefits reflected in the table, the Company also has unfunded, nonqualified benefit plans for executive officers and certain key management employees that generally provide for defined benefit payments at age 65 following the employee's retirement or, upon death, to their beneficiaries for a 15-year period. In February 2016, the Company froze the unfunded, nonqualified defined benefit plans to new participants and eliminated benefit increases. Vesting for participants not fully vested was retained. The Company's net periodic benefit cost for these plans for the three months ended March 31, 2017, was $1.2 million. The Company's net periodic benefit credit for these plans for the three months ended March 31, 2016, was$1.9 million, which reflects a curtailment gain of $3.3 million.