Accumulated Other Comprehensive Loss (Reclassifications out of Accumulated Other Comprehensive Loss to Net Income) (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Reclassification out of Accumulated Other Comprehensive Income [Line Items] | ||||
| Tax benefit | $ 28,240 | $ 37,025 | $ 105,356 | $ 117,489 |
| Reclassification out of Accumulated Other Comprehensive Income | Post-retirement plans | ||||
| Reclassification out of Accumulated Other Comprehensive Income [Line Items] | ||||
| Total before tax | 597 | 762 | 1,790 | 2,287 |
| Tax benefit | (234) | (281) | 703 | 892 |
| Net of tax | $ 363 | $ 481 | $ 1,087 | $ 1,395 |