STOCK-BASED COMPENSATION - Summary of restricted stock (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Non-performance based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares underlying restricted stock	178,831	161,443	211,153	181,773
Weighted-average grant date fair value per share	$ 28.04	$ 28.20	$ 27.85	$ 27.05
Aggregate fair value (in thousands)	$ 3,755
Weighted-average remaining vesting period (years)	2 years 4 months 24 days
Performance-based restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares underlying restricted stock	17,250	18,000	24,000	24,000
Weighted-average grant date fair value per share	$ 34.57	$ 34.46	$ 34.46	$ 34.46
Aggregate fair value (in thousands)	$ 362
Weighted-average remaining vesting period (years)	2 years 3 months 18 days

Weighted average remaining contractual term for equity based awards excluding options vesting term.

No definition available.

Name:	cbtx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsVestedWeightedAverageRemainingContractualTerm
Namespace Prefix:	cbtx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_AwardTypeAxis=cbtx_NonPerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: