Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Commitments to Extend Credit
Letters of credit	$ 2,118,278	$ 1,860,414
Accrued expenses and other liabilities
Commitments to Extend Credit
Allowance for unfunded credit commitments	29,000	11,100
Other Commitments
Unfunded commitments in investments in qualified affordable housing partnerships, tax credit and other investments	166,300	193,800
Single Family and Multi-family Residential Loans | Loans Sold or Securitized with Recourse | Accrued expenses and other liabilities | Loans Sold or Securitized With Recourse
Commitments to Extend Credit
Allowance for unfunded credit commitments	76	76
Standby Letters of Credit
Commitments to Extend Credit
Letters of credit	2,050,000	1,810,000
Commercial Letters of Credit
Commitments to Extend Credit
Letters of credit	$ 72,300	$ 48,500