Loans - Summary of Allowance for Loan Losses by Portfolio Class and Category (Details) - USD ($) $ in Thousands	3 Months Ended
Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Allowance for Loan Losses [Roll Forward]
Balance
Portfolio loans, net
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	42,007	$ 40,263	$ 38,166
Provision (provision reversal) for loan losses	2,332	2,385	1,871
Losses charged off	(2,595)	(1,027)	(1,035)
Recoveries	148	386	1,261
Balance	41,892	42,007	40,263
Portfolio loans, net \| Commercial and industrial
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	29,424	27,410	26,406
Provision (provision reversal) for loan losses	2,569	2,852	780
Losses charged off	(2,405)	(956)	(732)
Recoveries	2	118	956
Balance	29,590	29,424	27,410
Portfolio loans, net \| CRE - investor owned
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	4,561	4,546	3,890
Provision (provision reversal) for loan losses	3	5	648
Losses charged off	0	0	0
Recoveries	8	10	8
Balance	4,572	4,561	4,546
Portfolio loans, net \| CRE - owner occupied
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	3,845	3,502	3,308
Provision (provision reversal) for loan losses	(197)	340	190
Losses charged off	(22)	0	0
Recoveries	4	3	4
Balance	3,630	3,845	3,502
Portfolio loans, net \| Construction and land development
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	1,690	1,728	1,487
Provision (provision reversal) for loan losses	154	(206)	35
Losses charged off	0	0	0
Recoveries	21	168	206
Balance	1,865	1,690	1,728
Portfolio loans, net \| Residential real estate
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	1,763	2,315	2,237
Provision (provision reversal) for loan losses	(187)	(573)	259
Losses charged off	(122)	(38)	(254)
Recoveries	88	59	73
Balance	1,542	1,763	2,315
Portfolio loans, net \| Consumer and other
Allowance for Loan Losses [Roll Forward]
Balance at December 31, 2017	724	762	838
Provision (provision reversal) for loan losses	(10)	(33)	(41)
Losses charged off	(46)	(33)	(49)
Recoveries	25	28	14
Balance	$ 693	$ 724	$ 762

A valuation allowance for financing receivables that are expected to be uncollectible.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of direct write-downs of financing receivables charged against the allowance.

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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