Commitments and Contingencies (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) properties	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) properties	Sep. 30, 2017 USD ($)	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Number of non-cancelable operating leases | properties	216		216
Rent expense	$ 9,600	$ 9,700	$ 28,600	$ 28,900
Rent income	671	529	2,000	1,500
Standby letters of credit, financial guarantees required to perform on	0	0	0	0
Standby letters of credit that expire within one year	47,600		47,600
Standby letters of credit that expire thereafter	21,300		21,300
Standby letters of credit, fees	251	$ 218	590	$ 682
Residential mortgage loan repurchase reserve liability	1,400		$ 1,400
Days past due of GNMA loans available for repurchase			90 days
GNMA Loans past due by 90 days, but not yet repurchased	$ 8,000		$ 8,000
Real Estate Loans As Part Of Loan Portfolio
Concentration Risk [Line Items]
Concentration risk, percentage			75.00%		75.00%