Loans and Allowance for Loan Leases - Troubled Debt Restructuring Loans (Details) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020 USD ($) contract	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	$ 5,511	$ 4,761
Commitments to borrowers	$ 556		$ 934
Number of Loans \| contract	13		12
Outstanding Balance	$ 22,838		$ 39,543
Balance 90 days past due at any time during previous 12 months	842		831
Increase in allowance for loan losses from loan restructuring	$ 2,000		$ 18,000
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	6		7
Outstanding Balance	$ 9,966		$ 31,770
Balance 90 days past due at any time during previous 12 months	$ 842		$ 831
Energy
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	3		2
Outstanding Balance	$ 5,100		$ 2,864
Balance 90 days past due at any time during previous 12 months	$ 0		$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	3		3
Outstanding Balance	$ 4,772		$ 4,909
Balance 90 days past due at any time during previous 12 months	$ 0		$ 0
Construction and land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	0		0
Outstanding Balance	$ 0		$ 0
Balance 90 days past due at any time during previous 12 months	$ 0		$ 0
Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	1		0
Outstanding Balance	$ 3,000		$ 0
Balance 90 days past due at any time during previous 12 months	$ 0		$ 0
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans \| contract	0		0
Outstanding Balance	$ 0		$ 0
Balance 90 days past due at any time during previous 12 months	0		$ 0
Interest Rate Reduction \| Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	3,171	0
Reduction of Monthly Payment \| Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	0	4,761
Extension of Maturity Date \| Energy
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total troubled debt restructurings	$ 2,340	$ 0

Financing Receivable, Allowance For Credit Loss, Increase (Decrease) From Modification

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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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+ References

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Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

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-SubTopic 40
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-Paragraph 4
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
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- Definition

Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18794-111554

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