Pension Plan and Postretirement Benefits Other Than Pension (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Components of net periodic benefit cost:
Percentage of net periodic pension and other postretirement benefit costs included in Compensation and related costs	60.00%
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Final number of years of employee's compensation to determine the benefits payable	10 years
Employer contributions	$ 20,000,000
Components of net periodic benefit cost:
Service cost	3,047,000	2,725,000
Interest cost	2,154,000	2,153,000
Expected return on plan assets	(3,691,000)	(3,413,000)
Actuarial (gain) loss amortization	1,377,000	411,000
Prior service cost amortization	115,000	130,000
Transition obligation amortization	1,000	1,000
Total	3,003,000	2,007,000
Other Postretirement Benefits
Pension Plan and Postretirement Benefits Other than Pension
Age of employees after which the plan does not provide benefits	65 years
Components of net periodic benefit cost:
Service cost	228,000	180,000
Interest cost	99,000	99,000
Actuarial (gain) loss amortization		(4,000)
Prior service cost amortization	5,000	14,000
Total	$ 332,000	$ 289,000