Employee Benefit Plans (Details 2) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Dec. 31, 2015	Mar. 31, 2015	Mar. 31, 2014
Rate of compensation increase:
Compounded investment returns, period one (in years)	5 years
Compounded investment returns, period two (in years)	10 years
Pension Benefits
Components of net periodic benefit cost
Service cost	$ 14,445	$ 23,182	$ 34,763
Interest cost	91,044	129,236	130,253
Expected return on plan assets	(120,352)	(165,780)	(161,111)
Amortization of unrecognized net loss	112,949	118,163	145,891
Amortization of unrecognized prior service cost	(15,638)	(22,284)	(20,984)
Net periodic benefit cost before special termination benefits cost / curtailment	82,448	82,517	128,812
Special termination benefits cost / curtailment	0	2,469	0
Net periodic benefit cost	$ 82,448	$ 84,986	$ 128,812
Weighted-Average Assumptions Used to Determine Benefit Obligations
Discount rate (as a percent)	4.40%	3.90%	4.50%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost
Discount rate (as a percent)	3.90%	4.50%	4.35%
Expected long-term rate of return on plan assets (as a percent)	7.25%	7.25%	7.25%
Other Postretirement Benefits
Components of net periodic benefit cost
Service cost	$ 1	$ 3	$ 9
Interest cost	3,378	4,803	5,207
Expected return on plan assets	(2,767)	(3,553)	(3,419)
Amortization of unrecognized net loss	1,488	1,629	2,288
Amortization of unrecognized prior service cost	(5,439)	(8,362)	(8,381)
Net periodic benefit cost before special termination benefits cost / curtailment	(3,339)	(5,480)	(4,296)
Special termination benefits cost / curtailment	0	0	0
Net periodic benefit cost	$ (3,339)	$ (5,480)	$ (4,296)
Weighted-Average Assumptions Used to Determine Benefit Obligations
Discount rate (as a percent)	3.98%	3.55%	3.95%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost
Discount rate (as a percent)	3.55%	3.95%	3.80%
Equity Investment
Target asset allocation
Asset allocation percentage, minimum	20.00%
Asset allocation percentage, maximum	45.00%
Fixed Income Investment
Target asset allocation
Asset allocation percentage, minimum	35.00%
Asset allocation percentage, maximum	50.00%
Fixed Income Investment \| Pension Benefits
Target asset allocation
Asset allocation percentage, minimum	35.00%
Asset allocation percentage, maximum	50.00%
Real Estate
Target asset allocation
Asset allocation percentage, minimum	0.00%
Asset allocation percentage, maximum	10.00%
Real Estate \| Pension Benefits
Target asset allocation
Asset allocation percentage, minimum	0.00%
Asset allocation percentage, maximum	10.00%
Hedge Funds, Equity
Target asset allocation
Asset allocation percentage, minimum	15.00%
Asset allocation percentage, maximum	30.00%
Hedge Funds, Equity \| Pension Benefits
Target asset allocation
Asset allocation percentage, minimum	15.00%
Asset allocation percentage, maximum	30.00%
Cash Investment
Target asset allocation
Asset allocation percentage, minimum	0.00%
Asset allocation percentage, maximum	6.00%
Cash Investment \| Pension Benefits
Target asset allocation
Asset allocation percentage, minimum	0.00%
Asset allocation percentage, maximum	6.00%
5% Return \| Other Postretirement Benefits
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost
Expected long-term rate of return on plan assets (as a percent)	5.00%	5.00%	5.00%
6.25% Return \| Other Postretirement Benefits
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost
Expected long-term rate of return on plan assets (as a percent)	6.25%	6.25%	6.25%
Union employees \| Pension Benefits
Rate of compensation increase:
Compensation increase (as a percent)	3.13%	3.66%	3.22%
Rate of compensation increase:
Compensation increase (as a percent)	3.66%	3.22%	3.23%
Salaried employees \| Pension Benefits
Rate of compensation increase:
Compensation increase (as a percent)	3.62%	3.14%	3.47%
Rate of compensation increase:
Compensation increase (as a percent)	3.14%	3.47%	3.49%
Continuing Operations \| Pension Benefits
Components of net periodic benefit cost
Net periodic benefit cost	$ 82,448	$ 81,038	$ 120,812
Continuing Operations \| Other Postretirement Benefits
Components of net periodic benefit cost
Net periodic benefit cost	(3,339)	(5,496)	(4,340)
Discontinued Operations \| Pension Benefits
Components of net periodic benefit cost
Net periodic benefit cost	0	3,948	8,000
Discontinued Operations \| Other Postretirement Benefits
Components of net periodic benefit cost
Net periodic benefit cost	$ 0	$ 16	$ 44

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Represents the first historical period of compounded investment returns which is assessed in developing the expected long-term rate of return assumption.

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Represents the second historical period of compounded investment returns which is assessed in developing the expected long-term rate of return assumption.

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The total amount of net periodic benefit cost for defined benefit plans before net gain (loss) recognized due to curtailments recorded in net periodic benefit cost for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation.

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The amount of gains or losses recognized in net periodic benefit cost.

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The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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-Publisher FASB
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The interest rate used to adjust for the time value of money for the plan.

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Expected rate of compensation increases (for pay-related plans).

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The interest rate used to adjust for the time value of money.

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An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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Expected rate of compensation increases (for pay-related plans).

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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The amount of net gain (loss) recognized in net periodic benefit cost as a result of an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

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Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

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