Loans and Allowance for Loan Losses - Allowance for Credit Losses (Details) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 83,575,000	$ 67,240,000
Charged-off loans	(6,068,000)	(8,669,000)
Recovery of previously charged-off loans	2,503,000	4,702,000
Provision for loan losses	7,184,000	6,931,000
Ending Balance	87,194,000	70,204,000
Commercial real estate - mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	26,946,000	21,188,000
Charged-off loans	(534,000)	(728,000)
Recovery of previously charged-off loans	72,000	1,396,000
Provision for loan losses	3,683,000	832,000
Ending Balance	30,167,000	22,688,000
Consumer real estate - mortgage
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	7,670,000	5,031,000
Charged-off loans	(350,000)	(336,000)
Recovery of previously charged-off loans	369,000	666,000
Provision for loan losses	680,000	(261,000)
Ending Balance	8,369,000	5,100,000
Construction and land development
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	11,128,000	8,962,000
Charged-off loans	0	(2,000)
Recovery of previously charged-off loans	122,000	565,000
Provision for loan losses	(335,000)	591,000
Ending Balance	10,915,000	10,116,000
Commercial and industrial
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	31,731,000	24,863,000
Charged-off loans	(3,352,000)	(2,540,000)
Recovery of previously charged-off loans	1,598,000	888,000
Provision for loan losses	2,722,000	3,437,000
Ending Balance	32,699,000	26,648,000
Consumer and other
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	5,423,000	5,874,000
Charged-off loans	(1,832,000)	(5,063,000)
Recovery of previously charged-off loans	342,000	1,187,000
Provision for loan losses	870,000	3,478,000
Ending Balance	4,803,000	5,476,000
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	677,000	1,322,000
Charged-off loans	0	0
Recovery of previously charged-off loans	0	0
Provision for loan losses	(436,000)	(1,146,000)
Ending Balance	$ 241,000	$ 176,000

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

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