Loans and Allowance for Losses and Concentrations of Credit Risk - Certain Loans Acquired Delinquencies and Net Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	$ 26,881	$ 48,444
Net credit losses (recoveries)	40	(1,397)	$ 154
Certain Loans Acquired In Transfer Not Accounted For As Debt Securities, Subject To Be Purchased	100	300
On-balance sheet [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	19,577	47,881
Net credit losses (recoveries)	40	(1,397)	154
Off-balance sheet [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing Receivable, Recorded Investment, Past Due	7,304	563
Net credit losses (recoveries)	$ 0	$ 0	$ 0