Benefit Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Components of Net Periodic Benefit Cost [Abstract]
Estimated future employer contributions in current fiscal year	$ 17,000,000
Pension and Supplemental Executive Retirement Plans [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost	2,448,000	2,080,000
Interest Cost	3,908,000	4,009,000
Expected return on plan assets	(5,295,000)	(5,258,000)
Recognized net actuarial loss	1,209,000	291,000
Amortization of prior service cost	(211,000)	(42,000)
Net periodic benefit cost	2,059,000	1,080,000
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost [Abstract]
Service cost	202,000	177,000
Interest Cost	178,000	183,000
Expected return on plan assets	(1,248,000)	(1,161,000)
Recognized net actuarial loss	(35,000)	(73,000)
Amortization of prior service cost	(1,662,000)	(1,662,000)
Net periodic benefit cost	$ (2,565,000)	$ (2,536,000)