Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Commitments to Extend Credit
Letters of credit	$ 1,912,783	$ 1,796,647
Accrued expenses and other liabilities
Commitments to Extend Credit
Allowance for unfunded credit reserves	13,300	12,400
Other Commitments
Unfunded commitments in investments in qualified affordable housing partnerships, tax credit and other investments	135,900	161,000
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 reserves	87	$ 123
Standby Letters of Credit
Commitments to Extend Credit
Letters of credit	1,840,000
Commercial Letters of Credit
Commitments to Extend Credit
Letters of credit	$ 70,600