Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Guarantees
Letters of credit	$ 1,711,384	$ 1,655,897
Accrued expenses and other liabilities
Guarantees
Allowance for unfunded credit reserves	11,700	12,700
Other Commitments
Unfunded commitments in investments in qualified affordable housing partnerships, tax credit and other investments	144,400	169,200
Single Family and Multi-family Residential | Loans Sold or Securitized with Recourse
Guarantees
Total unpaid principal balance	107,500	113,700
Maximum potential future payments up to recourse component	50,200	38,700
Single Family and Multi-family Residential | Loans Sold or Securitized with Recourse | Accrued expenses and other liabilities
Guarantees
Allowance for unfunded credit reserves	181	$ 214
Standby Letters of Credit
Guarantees
Letters of credit	1,640,000
Commercial Letters of Credit
Guarantees
Letters of credit	$ 67,200