Commitments, Contingencies and Guarantees (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Potential Losses From Standby Letters Of Credit	$ 0
Undisbursed loan commitments	493,300,000	$ 571,000,000
Allowance for credit losses on lending-related commitments	$ 1,700,000	1,200,000
Consumer Price Index increase	1.90%
Standby Letters of Credit
Loss Contingencies [Line Items]
Face amount of off-balance sheet liability	$ 119,000,000	187,600,000
Commitments to Extend Credit
Loss Contingencies [Line Items]
Face amount of off-balance sheet liability	3,550,000,000	3,030,000,000
Performance guarantee
Loss Contingencies [Line Items]
Outstanding balance of loans	11,600,000	13,300,000
Maximum potential amount of undiscounted future payments	11,400,000	12,800,000
Recourse liability	100,000	200,000
SBA Guaranteed Notes | Performance guarantee
Loss Contingencies [Line Items]
Maximum potential amount of undiscounted future payments	19,100,000	20,600,000
Recourse liability	$ 1,200,000	$ 1,200,000