ALLOWANCE FOR LOAN LOSSES - Loan losses on the basis of Company's impairment methodology (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Allowance for loan losses on the basis of Company's impairment methodology
Loans individually evaluated for impairment	$ 13,463,000	$ 19,496,000
Loans collectively evaluated for impairment	2,636,415,000	2,433,633,000
Total	2,649,878,000	2,453,129,000
Allowance allocated to specific reserves for loans individually evaluated for impairment	796,000	758,000
Commercial and industrial
Allowance for loan losses on the basis of Company's impairment methodology
Loans individually evaluated for impairment	2,345,000	4,277,000
Loans collectively evaluated for impairment	537,739,000	515,502,000
Total	540,084,000	519,779,000
Commercial real estate
Allowance for loan losses on the basis of Company's impairment methodology
Loans individually evaluated for impairment	2,231,000	3,970,000
Loans collectively evaluated for impairment	852,282,000	791,763,000
Total	854,513,000	795,733,000
Construction and development
Allowance for loan losses on the basis of Company's impairment methodology
Loans collectively evaluated for impairment	559,672,000	515,533,000
Total	559,672,000	515,533,000
1-4 family residential
Allowance for loan losses on the basis of Company's impairment methodology
Loans individually evaluated for impairment	4,053,000	4,436,000
Loans collectively evaluated for impairment	277,472,000	277,575,000
Total	281,525,000	282,011,000
Multi‑family residential
Allowance for loan losses on the basis of Company's impairment methodology
Loans collectively evaluated for impairment	298,887,000	221,194,000
Total	298,887,000	221,194,000
Consumer
Allowance for loan losses on the basis of Company's impairment methodology
Loans individually evaluated for impairment	231,000
Loans collectively evaluated for impairment	39,572,000	39,421,000
Total	39,803,000	39,421,000
Agriculture
Allowance for loan losses on the basis of Company's impairment methodology
Loans collectively evaluated for impairment	9,923,000	11,076,000
Total	9,923,000	11,076,000
Other
Allowance for loan losses on the basis of Company's impairment methodology
Loans individually evaluated for impairment	4,603,000	6,813,000
Loans collectively evaluated for impairment	60,868,000	61,569,000
Total	$ 65,471,000	$ 68,382,000

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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=118936363&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118955202&loc=SL82895884-210446

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbtx_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbtx_ConstructionAndDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbtx_OneToFourFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbtx_MultiFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbtx_AgricultureLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbtx_OtherLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: