Variable Interest Entities - Unconsolidated VIEs (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Variable Interest Entity [Line Items]
Total commitments from the limited partners and general partners to the unconsolidated VIE	$ 23,522,838
Remaining unfunded commitments from the limited partners and general partners to the unconsolidated VIE	9,986,996
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Investments	649,626	$ 207,747
Fees receivable	29,202	30,384
Due from related parties	2,495	2,605
Total assets	1,136,519	473,529
Not Primary Beneficiary
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Investments	138,092	118,696
Fees receivable	4,133	8,703
Due from related parties	837	1,194
Total assets	143,062	128,593
Deferred incentive fee revenue	0	3,704
Non-controlling interests	(2,211)	(4,853)
Maximum exposure to loss	$ 140,851	$ 127,444