Commitments, Contingencies and Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Commitments to Extend Credit
Letters of credit	$ 2,240,000	$ 1,860,000
Allowance for Unfunded Credit Commitments	33,500	11,100
Other Commitments
Unfunded commitments for investments in AHP and other tax credit investments	182,726	7,190,625
Accrued Expenses And Other Liabilities
Other Commitments
Unfunded commitments for investments in AHP and other tax credit investments	182,700	193,800
Standby Letters of Credit
Commitments to Extend Credit
Letters of credit	2,120,000	1,810,000
Commercial Letters Of Credit
Commitments to Extend Credit
Letters of credit	124,900	48,500
Loans sold or securitized with recourse | Single Family Residential and Multi-Family Residential | Loans Sold or Securitized with Recourse
Commitments to Extend Credit
Allowance for Unfunded Credit Commitments	$ 88	$ 76