Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Subordinated Borrowing [Line Items]
Federal tax credits recognized in tax expense	$ 500	$ 430
Investment tax credits	1,920	$ 2,240
Investment carrying amount	7,511,931		$ 7,316,411
Unfunded capital and other commitments	6,576,172		6,385,741
Maximum exposure to loss, unconsolidated VIEs	50,092		52,106
Variable interest entity, primary beneficiary
Subordinated Borrowing [Line Items]
Investment carrying amount	53,330		53,610
Unfunded capital and other commitments	3,940		4,930
Variable interest entity, not primary beneficiary
Subordinated Borrowing [Line Items]
Investment carrying amount	20,209		22,742
Unfunded capital and other commitments	$ 25,981		$ 26,716