Condensed Consolidated Schedule of Investments (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Infrastructure Assets, Estimated Fair Value	$ 1,021,161	$ 983,552
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	64.70%	84.10%
Foreign Currency Forward Contracts, Estimated Fair Value	$ 4,437	$ 28
Foreign Currency Forward Contracts, Estimated Fair Value	(8,317)	(18,890)
Total Foreign Currency Forward Contracts	$ (3,880)	$ (18,862)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	(0.20%)	(1.60%)
Investments in Money Market Funds	$ 613,549	$ 278,417
Total Investments and Cash Equivalents, Estimated Fair Value	$ 1,630,830	$ 1,243,107
Total Investments and Cash Equivalents, Estimated Fair Value as a Percentage of Net Assets	103.40%	106.30%
Infrastructure assets investments, cost	$ 919,367	$ 895,257
Investments in Money Market Funds, cost	662,484	278,417
Investments and Cash Equivalents, cost	1,532,916	1,173,674
Money Market Funds
Investments in Money Market Funds	$ 613,549	$ 278,417
Investments in Money Market Funds, Estimated Fair Value as a Percentage of Net Assets	38.90%	23.80%
Investments in Money Market Funds, cost	$ 613,549	$ 278,417
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	91,000	91,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 329
Foreign Currency Forward Contracts, Estimated Fair Value		$ (1,222)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	(0.10%)
Nomura International PLC
Foreign Currency Forward Contracts, Notional	$ 91,000	$ 91,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 307
Foreign Currency Forward Contracts, Estimated Fair Value		$ (1,246)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	(0.10%)
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 123,000	$ 123,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 1,136
Foreign Currency Forward Contracts, Estimated Fair Value		$ (2,460)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.10%	(0.20%)
Nomura International PLC
Foreign Currency Forward Contracts, Notional	$ 123,000	$ 123,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 1,105
Foreign Currency Forward Contracts, Estimated Fair Value		$ (2,491)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.10%	(0.20%)
Barclays Bank PLC
Foreign Currency Forward Contracts, Notional	$ 9,000	$ 9,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 291	$ 28
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	0.00%
Nomura International PLC
Foreign Currency Forward Contracts, Notional	$ 74,500	$ 74,500
Foreign Currency Forward Contracts, Estimated Fair Value	$ (3,688)	$ (4,613)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	(0.20%)	(0.40%)
Barclays Bank PLC
Foreign Currency Forward Contracts, Notional	$ 74,500	$ 74,500
Foreign Currency Forward Contracts, Estimated Fair Value	$ (3,706)	$ (4,631)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	(0.20%)	(0.40%)
Royal Bank of Canada
Foreign Currency Forward Contracts, Notional	$ 27,400	$ 27,400
Foreign Currency Forward Contracts, Estimated Fair Value	$ (775)	$ (1,115)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	(0.10%)
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 6,200	$ 6,200
Foreign Currency Forward Contracts, Estimated Fair Value	$ (148)	$ (225)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	0.00%
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 5,600	$ 5,600
Foreign Currency Forward Contracts, Estimated Fair Value	$ 56
Foreign Currency Forward Contracts, Estimated Fair Value		$ (58)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	0.00%
Nomura International PLC
Foreign Currency Forward Contracts, Notional	$ 36,300	$ 36,300
Foreign Currency Forward Contracts, Estimated Fair Value	$ 254
Foreign Currency Forward Contracts, Estimated Fair Value		$ (808)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	(0.10%)
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 9,000	$ 9,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 90
Foreign Currency Forward Contracts, Estimated Fair Value		$ (21)
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%	0.00%
Nomura International PLC
Foreign Currency Forward Contracts, Notional	$ 10,500
Foreign Currency Forward Contracts, Estimated Fair Value	$ 18
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%
Nomura International PLC
Foreign Currency Forward Contracts, Notional	$ 57,000
Foreign Currency Forward Contracts, Estimated Fair Value	$ 666
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 15,500
Foreign Currency Forward Contracts, Estimated Fair Value	$ 155
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 6,300
Foreign Currency Forward Contracts, Estimated Fair Value	$ 25
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%
Goldman, Sachs & Co.
Foreign Currency Forward Contracts, Notional	$ 10,300
Foreign Currency Forward Contracts, Estimated Fair Value	$ 5
Foreign Currency Forward Contracts, Estimated Fair Value as a Percentage of Net Assets	0.00%
Morgan Stanley Institutional Liquidity Funds Government Portfolio | Money Market Funds
Investments in Money Market Funds	$ 613,549	$ 278,417
Investments in Money Market Funds, Estimated Fair Value as a Percentage of Net Assets	38.90%	23.80%
Digital Infrastructure
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	8.30%	10.00%
Digital Infrastructure | Vantage Towers AG | EMEA
Infrastructure Assets, Estimated Fair Value	$ 113,350	$ 111,983
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	7.20%	9.60%
Digital Infrastructure | Other Infrastructure Assets | Asia-Pacific
Infrastructure Assets, Estimated Fair Value	$ 17,331	$ 4,689
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	1.10%	0.40%
Energy Security
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	11.30%	14.70%
Energy Security | Other Infrastructure Assets | North America
Infrastructure Assets, Estimated Fair Value	$ 24,300	$ 16,830
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	1.50%	1.40%
Energy Security | Pembina Gas Infrastructure Inc. | North America
Infrastructure Assets, Estimated Fair Value	$ 153,690	$ 156,178
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	9.70%	13.30%
Energy Transition
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	12.60%	15.60%
Energy Transition | Other Infrastructure Assets | EMEA
Infrastructure Assets, Estimated Fair Value	$ 15,725	$ 9,015
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	1.00%	0.80%
Energy Transition | Albioma SA | EMEA
Infrastructure Assets, Estimated Fair Value	$ 182,453	$ 173,823
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	11.60%	14.90%
Industrial Infrastructure
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	10.70%	14.70%
Industrial Infrastructure | Refresco Group B.V. | EMEA
Infrastructure Assets, Estimated Fair Value	$ 168,175	$ 172,087
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	10.70%	14.70%
Social Infrastructure
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	21.90%	29.00%
Social Infrastructure | Grove Education Partners Holdco Limited | EMEA
Infrastructure Assets, Estimated Fair Value	$ 346,137	$ 338,947
Infrastructure Assets, Estimated Fair Value as a Percentage of Net Assets	21.90%	29.00%