Pension Benefits (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net periodic benefit cost:
Service cost	$ 600,000	$ 600,000	$ 1,200,000	$ 1,200,000
Interest cost	2,242,000	2,301,000	4,484,000	4,601,000
Expected return on plan assets	(3,117,000)	(3,356,000)	(6,233,000)	(6,711,000)
Amortization of net actuarial loss	247,000	235,000	494,000	470,000
Total net periodic benefit	$ (28,000)	$ (220,000)	$ (55,000)	$ (440,000)
Weighted average assumptions used to determine net cost
Discount rate	4.10%	3.80%	4.10%	3.80%
Expected return on plan assets	7.25%	7.25%	7.25%	7.25%
Employer contributions			$ 3,000,000	$ 3,000,000