Commitments and Contingencies (Narrative) (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) properties	Mar. 31, 2017 USD ($)	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Number of non-cancelable operating leases | properties	225
Rent expense	$ 9,600	$ 9,800
Rent income	684	513
Standby letters of credit, financial guarantees required to perform on	0	0
Standby letters of credit that expire within one year	39,100
Standby letters of credit that expire thereafter	30,900
Standby letters of credit, fees	113	$ 154
Residential mortgage loan repurchase reserve liability	$ 1,400
Days past due of GNMA loans available for repurchase	90 days
GNMA Loans past due by 90 days, but not yet repurchased	$ 6,300
Real Estate Loans As Part Of Loan Portfolio
Concentration Risk [Line Items]
Concentration risk, percentage	75.00%		75.00%