Significant Accounting Policies - Investments in Unconsolidated Entities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 31, 2020
Investments in Unconsolidated Entities
Carrying value	$ 21,215	$ 23,182
Water Services and Land Company No. 1 | Water solutions | Operating segment
Investments in Unconsolidated Entities
Ownership interest	50.00%
Carrying value	$ 15,082	16,607
Water Services and Land Company No. 2 | Water solutions | Operating segment
Investments in Unconsolidated Entities
Ownership interest	50.00%
Carrying value	$ 1,926	2,092
Water Services and Land Company No. 3 | Water solutions | Operating segment
Investments in Unconsolidated Entities
Ownership interest	10.00%
Carrying value	$ 2,846	3,384
Aircraft Company | Corporate and other | Operating segment
Investments in Unconsolidated Entities
Ownership interest	50.00%
Carrying value	$ 751	447
Water Services Company | Water solutions | Operating segment
Investments in Unconsolidated Entities
Ownership interest	50.00%
Carrying value	$ 435	449
Natural Gas Liquids Terminal Company | Liquids and refined products | Operating segment
Investments in Unconsolidated Entities
Ownership interest	50.00%
Carrying value	$ 175	$ 203