Variable Interest Entities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subordinated notes
Federal tax credits recognized in tax expense	$ 1,720	$ 1,550	$ 1,290
Investment tax credits	31,080	15,860	$ 10,450
Investment carrying amount	7,316,411	6,622,776
Unfunded capital and other commitments	6,385,741	5,774,140
Unconsolidated maximum exposure to loss	52,106	37,904
Variable interest entity, primary beneficiary
Subordinated notes
Investment carrying amount	53,610	41,240
Unfunded capital and other commitments	4,930	18,680
Variable interest entity, not primary beneficiary
Subordinated notes
Investment carrying amount	22,742	19,843
Unfunded capital and other commitments	$ 26,716	$ 17,420