Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Subordinated Borrowing [Line Items]
Federal tax credits recognized in tax expense	$ 510	$ 430	$ 1,010	$ 860
Investment tax credits	1,080	$ 5,600	3,000	$ 7,840
Investment carrying amount	7,718,694		7,718,694		$ 7,316,411
Unfunded capital and other commitments	6,773,237		6,773,237		6,385,741
Maximum exposure to loss, unconsolidated VIEs	60,713		60,713		52,106
Variable interest entity, primary beneficiary
Subordinated Borrowing [Line Items]
Investment carrying amount	53,070		53,070		53,610
Unfunded capital and other commitments	3,940		3,940		4,930
Variable interest entity, not primary beneficiary
Subordinated Borrowing [Line Items]
Investment carrying amount	20,313		20,313		22,742
Unfunded capital and other commitments	$ 14,575		$ 14,575		$ 26,716