Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Commitments to Extend Credit
Letters of credit	$ 2,340,000	$ 2,240,000
Allowance for unfunded credit commitments	32,400	33,500
Accrued expenses and other liabilities
Other Commitments
Unfunded commitments for investments in AHP and other tax credit investments	334,700	182,700
Single Family and Multi-family Residential Loans | Loans Sold or Securitized with Recourse | Loans Sold or Securitized With Recourse
Commitments to Extend Credit
Allowance for unfunded credit commitments	83	88
Standby Letters of Credit
Commitments to Extend Credit
Letters of credit	2,220,000	2,120,000
Commercial Letters of Credit
Commitments to Extend Credit
Letters of credit	$ 125,000	$ 124,900