Loans and Allowances for Credit Losses, Troubled Debt Restructurings (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 152,000	$ 169,000	$ 152,000	$ 169,000	$ 126,000
Troubled Debt Restructuring, Performing in Accordance With Modified Terms	80,000	71,000	80,000	71,000	48,000
Financing Receivable, Modifications, Post-Modification Recorded Investment	19,000	34,000	32,000	53,000
Troubled Debt Restructuring, Charge-offs	5,500	10	5,600	42
Permanent mortgages guaranteed by US government agencies [Member] | Accruing [Member] | Residential mortgage
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructuring, Recorded Investment	$ 75,000	$ 81,000	$ 75,000	$ 81,000	$ 74,000