Other Real Estate Owned and Repossessed Assets - Rollforward Tables (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017		Dec. 31, 2016	[2]
Repossessed Assets [Line Items]
Cumulative effect adjustment of change in accounting policy, net of tax impact			$ 1,339	[1]	$ 3,659
Changes in other real estate owned
Balance at the beginning of the period	$ 8,182	$ 16,812
Transfers out based on new accounting adoption	(189)
Other additions	5,281	5,339
Net payments received	(190)	(582)
Disposals	(5,859)	(10,180)
Write-downs	(1,207)	(1,323)
Balance at the end of the period	6,018	10,066
Changes in repossessed assets
Balance at the beginning of the period	625	375
Transfers out based on new accounting adoption	0
Other additions	3,504	3,633
Net payments received	0	0
Disposals	(3,563)	(3,469)
Write-downs	0	0
Balance at the end of the period	566	$ 539
Retained earnings
Repossessed Assets [Line Items]
Cumulative effect adjustment of change in accounting policy, net of tax impact			1,680	[1]	$ 3,659
ASU 2014-09
Repossessed Assets [Line Items]
Loans to facilitate reclassified to loans	$ 1,100
ASU 2014-09 | Retained earnings
Repossessed Assets [Line Items]
Cumulative effect adjustment of change in accounting policy, net of tax impact			$ 900

[1] Refer to Note 1, Basis of Presentation and Significant Accounting Policies, Note 3, Investment Securities, Note 5, Other Real Estate Owned and Repossessed Assets and Note 9, Derivative Instruments and Balance Sheet Offsetting, for further details on the changes in accounting policy.

[2] Refer to Note 1, Basis of Presentation and Significant Accounting Policies and Note 7, Loan Servicing Rights for further details on the changes in accounting policy.