Guarantees (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Guarantee Obligations [Line Items]
Acquired standby letters of credit and financial guarantees	$ 21,100,000	$ 4,000,000
Unpaid principal balance of residential subject loans subject to credit recourse	6,400,000	20,100,000
Repurchased GNMA	107,000	515,000
Liability for estimated credit losses to loans sold with credit recourse	358,000	710,000
Repurchased loans not subject to credit recourse provision	3,100,000	3,700,000
Losses from repurchased loans subject to credit recourse	260,000	380,000	$ 1,400,000
Losses On Repurchased Loan Not Subject To Credit Recourse	477,000	1,300,000	$ 2,500,000
Serviced mortgage loans for third parties	864,900,000
Funds Advanced To Investors Under Servicing Agreements	$ 440,000	$ 334,000