COMMITMENTS AND CONTINGENCIES, INCLUDING FINANCIAL INSTRUMENTS WITH OFF-BALANCE-SHEET RISK - Contingent Liabilities (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)
Contingent Liabilities
Number of private investment funds under the Small Business Investment Company (SBIC) program \| item	2
Unfunded commitments	$ 3.8	$ 4.0
Cumulative capital contributions	$ 1.6	$ 1.5

Number of private investment funds under the Small Business Investment Company (SBIC) program of the U.S. Small Business Administration.

No definition available.

Name:	cbtx_NumberOfPrivateInvestmentsFundsUnderSmallBusinessInvestmentCompanyProgram
Namespace Prefix:	cbtx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration