Pension Benefit and Other Postretirement Benefit Plans - Additional Information (Details) (USD $)	4 Months Ended		3 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended		4 Months Ended		12 Months Ended		4 Months Ended			4 Months Ended
	Apr. 30, 2013	Jun. 30, 2013	Jun. 30, 2013 Retirement Health and Life Insurance Benefits [Member]	Jun. 30, 2012 Retirement Health and Life Insurance Benefits [Member]	Mar. 31, 2012 Retirement Health and Life Insurance Benefits [Member]	Jun. 30, 2013 Retirement Health and Life Insurance Benefits [Member]	Jun. 30, 2012 Retirement Health and Life Insurance Benefits [Member]	Jun. 30, 2013 Pension Benefits [Member]	Jun. 30, 2012 Pension Benefits [Member]	Jun. 30, 2013 Pension Benefits [Member]	Jun. 30, 2012 Pension Benefits [Member]	Apr. 30, 2013 Equity Securities [Member]	Apr. 30, 2013 Debt Securities [Member]	Dec. 31, 2012 Rate of return on plan assets over the next 5 year period [Member]	Apr. 30, 2013 Rate of return on plan assets over the next 5 year period [Member]	Apr. 30, 2013 Rate of return on plan assets over the next 7 year period [Member]	Apr. 30, 2013 Hypothetical rates of return on plan assets for a 10 year period [Member]	Apr. 30, 2013 Historical performance of plan assets over a 16 year period [Member]	Apr. 30, 2013 Hypothetical rates of return on plan assets for a 20 year period [Member]	Apr. 30, 2013 Hypothetical rates of return on plan assets for a 30 year period [Member] [Member]	Apr. 30, 2013 Fixed Income Securities [Member] Rate of return on plan assets over the next 5 year period [Member]	Apr. 30, 2013 Fixed Income Securities [Member] Rate of return on plan assets over the next 7 year period [Member]	Apr. 30, 2013 Equity Securities [Member] Rate of return on plan assets over the next 5 year period [Member]	Apr. 30, 2013 Equity Securities [Member] Rate of return on plan assets over the next 7 year period [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Projected benefit obligation of plan assets with accumulated benefit obligation in excess of plan assets		$ 191,400,000
Accumulated benefit obligation of plan assets with accumulated benefit obligation in excess of plan assets		191,400,000
Fair value of plan assets with accumulated benefit obligation in excess of plan assets		157,400,000
Settlement charge/(credit)								1,537,000		1,537,000
Special termination benefit				(707,000)	2,300,000		1,593,000
Target plan asset allocations												57.00%	43.00%
Expected return on plan assets	0.086							2,731,000	2,495,000	5,447,000	4,903,000			0.073		0.078	0.080		0.081	0.102	0.0350	0.0450	0.095	0.110
Number of Years															10 years	15 years	10 years	16 years	20 years	30 years
Employer voluntary contributions										$ 6,500,000	$ 16,000,000