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Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2024
Feb. 18, 2025
Jun. 28, 2024
Cover [Abstract]      
Entity Registrant Name CSG SYSTEMS INTERNATIONAL, INC.    
Entity Central Index Key 0001005757    
Document Type 10-K    
Document Period End Date Dec. 31, 2024    
Amendment Flag false    
Entity Small Business false    
Entity Emerging Growth Company false    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY    
Trading Symbol CSGS    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Public Float     $ 844,833,184
Entity Common Stock, Shares Outstanding   28,839,469  
Entity Current Reporting Status Yes    
Entity Shell Company false    
ICFR Auditor Attestation Flag true    
Entity File Number 0-27512    
Entity Tax Identification Number 47-0783182    
Entity Address, Address Line One 169 Inverness Dr W    
Entity Address, Address Line Two Suite 300    
Entity Address, City or Town Englewood    
Entity Address, State or Province CO    
Entity Address, Postal Zip Code 80112    
City Area Code (303)    
Local Phone Number 200-2000    
Entity Incorporation, State or Country Code DE    
Document Annual Report true    
Document Transition Report false    
Document Financial Statement Error Correction [Flag] false    
Title of 12(b) Security Common Stock, Par Value $0.01 Per Share    
Security Exchange Name NASDAQ    
Entity Interactive Data Current Yes    
Documents Incorporated by Reference Portions of the registrant’s Definitive Proxy Statement for its 2025 Annual Meeting of Stockholders, to be filed on or prior to April 30, 2025, are incorporated by reference into Part III of this Annual Report on Form 10-K.    
Auditor Firm ID 185    
Auditor Name KPMG LLP    
Auditor Location Omaha, Nebraska    
Auditor Opinion [Text Block]

We have audited CSG Systems International, Inc. and subsidiaries' (the Company) internal control over financial reporting as of December 31, 2024, based on criteria established in Internal Control – Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission. In our opinion, the Company maintained, in all material respects, effective internal control over financial reporting as of December 31, 2024, based on criteria established in Internal Control – Integrated Framework (2013) issued by the Committee of Sponsoring Organizations of the Treadway Commission.

We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the consolidated balance sheets of the Company as of December 31, 2024 and 2023, the related consolidated statements of income, comprehensive income, stockholders’ equity, and cash flows for each of the years in the three-year period ended December 31, 2024, and the related notes (collectively, the consolidated financial statements), and our report dated February 20, 2025 expressed an unqualified opinion on those consolidated financial statements.