Investments - Summarized Financial Information of Equity Method Investment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Assets
Investments	$ 649,626				$ 207,747				$ 649,626	$ 207,747
Other assets	17,821				17,675				17,821	17,675
Total assets	1,136,519				473,529				1,136,519	473,529
Liabilities and Partners’ Capital
Debt	163,175				74,524				163,175	74,524
Other liabilities	36,122				22,132				36,122	22,132
Total liabilities	546,318				236,128				546,318	236,128
Partners’ capital	314,201				237,401				314,201	237,401
Total liabilities, redeemable non-controlling interests and equity	1,136,519				473,529				1,136,519	473,529
Net Income
Net income	64,586	$ 54,632	$ 44,599	$ 4,968	38,613	$ 28,437	$ 32,273	$ 27,453	168,785	126,776	$ 98,997
Partnerships
Assets
Investments	22,445,159				17,577,766				22,445,159	17,577,766
Other assets	610,672				415,221				610,672	415,221
Total assets	23,055,831				17,992,987				23,055,831	17,992,987
Liabilities and Partners’ Capital
Debt	11,838				61,114				11,838	61,114
Other liabilities	116,593				107,600				116,593	107,600
Total liabilities	128,431				168,714				128,431	168,714
Partners’ capital	22,927,400				17,824,273				22,927,400	17,824,273
Total liabilities, redeemable non-controlling interests and equity	$ 23,055,831				$ 17,992,987				23,055,831	17,992,987
Net Income
Investment income									389,571	300,121	211,797
Total expenses									201,791	185,769	149,598
Net investment income									187,780	114,352	62,199
Net realized and unrealized gain									3,232,126	1,830,599	618,047
Net income									$ 3,419,906	$ 1,944,951	$ 680,246