Pension Benefits (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net periodic benefit cost:
Service cost	$ 600,000	$ 400,000	$ 1,800,000	$ 1,600,000
Interest cost	2,209,000	2,258,000	6,693,000	6,859,000
Expected return on plan assets	(3,129,000)	(3,364,000)	(9,362,000)	(10,075,000)
Amortization of net actuarial loss	219,000	205,000	713,000	675,000
Total net periodic benefit	$ (101,000)	$ (501,000)	$ (156,000)	$ (941,000)
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			$ 6,000,000	$ 6,000,000