Pension Plan and Other Postretirement Benefits (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Plan and Other Postretirement Benefits
Cash payments by the entity related to pension plans and other postretirement benefits	$ 7,700,000	$ 7,500,000
Pension plans
Components of the pension plans and other postretirement benefits
Estimated cash contributions in the current fiscal year	26,800,000
Service cost	4,217,000	4,658,000
Interest cost	4,726,000	4,063,000
Expected return on plan assets	(4,179,000)	(3,565,000)
Amortization of prior service cost	1,510,000	1,541,000
Recognized net actuarial loss	1,003,000	2,224,000
Net periodic benefit cost	7,277,000	8,921,000
Other Benefits
Components of the pension plans and other postretirement benefits
Estimated cash contributions in the current fiscal year	9,600,000
Service cost	1,619,000	1,695,000
Interest cost	1,337,000	1,109,000
Expected return on plan assets	(753,000)	(598,000)
Recognized net initial APBO		2,000
Amortization of prior service cost	11,000	20,000
Recognized net actuarial loss	775,000	916,000
Net periodic benefit cost	$ 2,989,000	$ 3,144,000