Investment Partnerships and Other Entities, Equity Method Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Investments In Affiliated and Unaffiliated Entities [Abstract]
Investments in unaffiliated entities	$ 41,900	$ 24,900
Investments in affiliated entities	112,600	99,100
Summarized Financial Information [Abstract]
Total assets	1,203,336	1,174,545
Total liabilities	65,534	66,328
Total equity	935,346	901,389	$ 931,188	$ 932,465	$ 915,746	$ 854,167	$ 852,687	$ 820,803	$ 897,435
Net income/(loss)	59,203	18,816
Equity Method Investment [Member]
Summarized Financial Information [Abstract]
Total assets	1,818,000	1,653,000
Total liabilities	358,000	326,000
Total equity	1,460,000	1,327,000
Net income/(loss)	$ 239,000	$ 64,000
Unaffiliated [Member] | Minimum [Member]
Summarized Financial Information [Abstract]
Notice period for redeeming investments	30 days
Unaffiliated [Member] | Maximum [Member]
Summarized Financial Information [Abstract]
Notice period for redeeming investments	95 days