Employee benefit plans

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Pension and other postretirement benefit plans

Employee benefit plans

Pension and other postretirement plans

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

	Pension Benefits						Other Postretirement Benefits
Three Months Ended June 30,	2018			2017			2018			2017
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	340		$	306
Interest cost	3,488			4,089			672			825
Expected return on assets	(5,379		)	(5,234		)	(1,266		)	(1,175		)
Amortization of prior service credit	—			—			(348		)	(343		)
Amortization of net actuarial loss	1,721			1,385			82			100
Net periodic benefit cost (credit), including amount capitalized	(170		)	240			(520		)	(287		)
Less amount capitalized	—			73			43			(114		)
Net periodic benefit cost (credit)	$	(170	)	$	167		$	(563	)	$	(173	)

	Pension Benefits						Other Postretirement Benefits
Six Months Ended June 30,	2018			2017			2018			2017
	(In thousands)
Components of net periodic benefit cost (credit):
Service cost	$	—		$	—		$	747		$	753
Interest cost	7,295			8,103			1,450			1,633
Expected return on assets	(10,377		)	(10,263		)	(2,433		)	(2,320		)
Amortization of prior service credit	—			—			(697		)	(686		)
Amortization of net actuarial loss	3,503			3,178			320			436
Net periodic benefit cost (credit), including amount capitalized	421			1,018			(613		)	(184		)
Less amount capitalized	—			180			83			(153		)
Net periodic benefit cost (credit)	$	421		$	838		$	(696	)	$	(31	)

In accordance with ASU 2017-07, the components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income.

Nonqualified defined benefit plans

In addition to the qualified defined benefit pension plans reflected in the table, the Company also has unfunded, nonqualified defined 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 and six months ended June 30, 2018, was $1.1 million and $2.2 million, respectively. The Company's net periodic benefit cost for these plans for the three and six months ended June 30, 2017, was $1.1 million and $2.3 million , respectively. In accordance with ASU 2017-07, the components of net periodic benefit cost for these plans, which does not contain any service costs, have been classified as other income on the Consolidated Statements of Income.