Pension Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net periodic benefit cost:
Service cost	$ 338	$ 400
Interest cost	2,002	1,849
Expected return on plan assets	(3,330)	(3,438)
Amortization of net actuarial loss	191	179
Total net periodic benefit	$ (799)	$ (1,010)
Weighted average assumptions used to determine net cost
Discount rate	4.05%	3.45%
Expected return on plan assets	7.25%	7.25%
Employer contributions	$ 1,500	$ 1,500