Allowance for Loan Losses - Allowance for Loan Loss Individually and Collectively Evaluated by Portfolio Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	$ 2,601	$ 2,420
Collectively evaluated	26,962	27,128
Allowance for loan losses	29,772	29,831	$ 26,464	$ 25,450
Individually evaluated	65,363	51,477
Collectively evaluated	3,488,972	3,213,532
Loans	3,580,966	3,302,264
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	839	993
Collectively evaluated	6,935	8,101
Allowance for loan losses	7,846	9,331	8,582	10,152
Individually evaluated	24,333	20,300
Collectively evaluated	766,143	738,297
Loans	811,199	784,737
SBA
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	294	156
Collectively evaluated	1,674	1,822
Allowance for loan losses	1,968	1,978	2,433	3,015
Individually evaluated	6,797	13,331
Collectively evaluated	133,955	122,662
Loans	141,208	149,779
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	0	0
Collectively evaluated	2,371	2,151
Allowance for loan losses	2,396	2,176	1,711	1,486
Individually evaluated	4,520	6,394
Collectively evaluated	243,344	229,907
Loans	248,317	238,910
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	219	235
Collectively evaluated	10,539	9,570
Allowance for loan losses	10,758	9,812	8,668	6,591
Individually evaluated	453	398
Collectively evaluated	1,741,635	1,592,261
Loans	1,742,151	1,592,868
Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	1,249	1,036
Collectively evaluated	4,567	4,705
Allowance for loan losses	5,928	5,755	4,294	3,475
Individually evaluated	29,260	14,384
Collectively evaluated	603,895	513,821
Loans	638,091	535,970
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated	0	0
Collectively evaluated	876	779
Allowance for loan losses	876	779	$ 776	$ 731
Individually evaluated	0	0
Collectively evaluated	0	0
Loans	0	0
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	209	283
Loans	26,631	37,255
Receivables Acquired with Deteriorated Credit Quality \| Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	72	237
Loans	20,723	26,140
Receivables Acquired with Deteriorated Credit Quality \| SBA
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	0	0
Loans	456	532
Receivables Acquired with Deteriorated Credit Quality \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	25	25
Loans	453	2,609
Receivables Acquired with Deteriorated Credit Quality \| Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	0	7
Loans	63	209
Receivables Acquired with Deteriorated Credit Quality \| Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	112	14
Loans	4,936	7,765
Receivables Acquired with Deteriorated Credit Quality \| Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	0	0
Loans	$ 0	$ 0

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

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)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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Period Type:	instant

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

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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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ 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 (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ 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 (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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