Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Subordinated Borrowing [Line Items]
Federal tax credits recognized in tax expense	$ 550	$ 430	$ 1,560	$ 1,290
Investment tax credits	320	$ 0	3,320	$ 7,840
Investment carrying amount	7,964,092		7,964,092		$ 7,316,411
Unfunded capital and other commitments	7,007,695		7,007,695		6,385,741
Maximum exposure to loss, unconsolidated VIEs	57,804		57,804		52,106
Variable interest entity, primary beneficiary
Subordinated Borrowing [Line Items]
Investment carrying amount	58,970		58,970		53,610
Unfunded capital and other commitments	8,910		8,910		4,930
Variable interest entity, not primary beneficiary
Subordinated Borrowing [Line Items]
Investment carrying amount	31,339		31,339		22,742
Unfunded capital and other commitments	$ 25,829		$ 25,829		$ 26,716