Loans and Allowance for Credit Losses - Summary of Consumer Credit Exposure on ACI loans, Based on Past Due Status (Details) - ACI Loans - Consumer - USD ($) $ in Thousands		Dec. 31, 2018		Dec. 31, 2017
Residential Real Estate
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		$ 122,639	[1]	$ 152,336
Residential Real Estate | 0-29 DPD
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		115,404	[1]	139,662
Residential Real Estate | 30-59 DPD
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		1,985	[1]	2,299
Residential Real Estate | 60-89 DPD
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		1,435	[1]	2,496
Residential Real Estate | Financing Receivables 90 to 119 Days Past Due
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		217	[1]	399
Residential Real Estate | Financing Receivables 120 Days Past Due
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		3,598	[1]	7,480
Other
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		939	[1]	1,583
Other | 0-29 DPD
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		845	[1]	1,356
Other | 30-59 DPD
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due		91	[1]	120
Other | 60-89 DPD
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due				62
Other | Financing Receivables 90 to 119 Days Past Due
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due	[1]	$ 3
Other | Financing Receivables 120 Days Past Due
Accounts Notes And Loans Receivable [Line Items]
Loans Past Due				$ 45

[1] During the third quarter of 2018, the Company began determining the risk rating classification for its consumer portfolio based on delinquency and nonaccrual status in accordance with the Uniform Retail Credit Classification guidance, which contributed to a lower amount of nonaccrual loans from the previous periods.