Retirement Benefits (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Net Periodic Pension Benefit Cost:
Employer contribution	$ 15,900,000
Pension
Net Periodic Pension Benefit Cost:
Service cost	1,868,000	1,628,000	6,500,000	5,830,000
Interest cost	2,509,000	2,551,000	10,215,000	10,366,000
Expected return on plan assets	(3,125,000)	(3,076,000)	(12,358,000)	(11,534,000)
Amortization of prior service cost	133,000	133,000	532,000	532,000
Amortization of net actuarial loss	2,590,000	1,950,000	8,576,000	6,091,000
Net periodic benefit cost	3,975,000	3,186,000	13,465,000	11,285,000
SERP
Net Periodic Pension Benefit Cost:
Service cost	15,000	7,000	59,000	81,000
Interest cost	63,000	56,000	270,000	198,000
Amortization of prior service cost	(2,000)	(2,000)	(8,000)	(8,000)
Amortization of net actuarial loss	104,000	76,000	416,000	213,000
Net periodic benefit cost	180,000	137,000	737,000	484,000
OPEB
Net Periodic Pension Benefit Cost:
Service cost	755,000	565,000	2,591,000	2,205,000
Interest cost	992,000	1,032,000	3,996,000	4,286,000
Expected return on plan assets	(1,099,000)	(1,041,000)	(4,193,000)	(4,148,000)
Amortization of prior service cost	(253,000)	(253,000)	(1,011,000)	(1,011,000)
Amortization of net actuarial loss	649,000	468,000	1,844,000	1,729,000
Net periodic benefit cost	$ 1,044,000	$ 771,000	$ 3,227,000	$ 3,061,000