v3.26.1
Securities - Additional Information (Details)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2026
USD ($)
Security
shares
Jun. 30, 2025
USD ($)
Jun. 30, 2026
USD ($)
Segment
Security
Jun. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Security
Schedule Of Held To Maturity Securities [Line Items]          
Number of Investment Securities Segments | Segment     2    
Credit losses     $ 0    
Municipal securities percentage of securities portfolio 1.00%   1.00%    
Securities in Unrealized Loss Positions Qualitative Disclosure Number of Positions Greater Than or Equal to One Year | Security 647   647   712
Gain (loss) on sale of investment securities $ (4,000,000) $ 0 $ (4,000,000) $ 0  
Available for Sale Securities, Amortized Cost Basis 346,342,000   346,342,000   $ 338,572,000
Debt Securities, Available-for-Sale 346,023,000   346,023,000   338,197,000
Collateralized Securities [Member]          
Schedule Of Held To Maturity Securities [Line Items]          
Available for Sale Securities, Amortized Cost Basis 10,230,000,000   10,230,000,000   9,240,000,000
Debt Securities, Available-for-Sale 9,430,000,000   $ 9,430,000,000   $ 8,430,000,000
Visa Stock Exchange [Member]          
Schedule Of Held To Maturity Securities [Line Items]          
Conversion of stock, description     During the second quarter of 2026, the Company tendered all of its shares of Visa, Inc. (“Visa”) Class B-2 common stock in exchange for a combination of Visa Class B-3 common stock and Visa Class C common stock, pursuant to the terms and subject to the conditions of Visa’s public exchange offer, which expired on May 8, 2026. The Company recorded an unrealized gain of $12.2 million during the second quarter 2026 based on the conversion privilege of the Class C common stock and the closing price of Visa Class A common stock. In the exchange, the Company received 24,246 shares of Class B-3 stock, recorded at zero cost basis, and 9,137 shares of Class C common stock and subsequently sold 3,045 shares of Class C stock. Prosperity intends to sell all remaining shares of Class C stock as permitted by the exchange agreement.    
Gain on stock exchange $ 12,200,000        
Class B-2 Common Stock [Member] | Visa Stock Exchange [Member]          
Schedule Of Held To Maturity Securities [Line Items]          
Conversion of stock, shares converted | shares 24,246        
Cost basis $ 0        
Common Class C [Member] | Visa Stock Exchange [Member]          
Schedule Of Held To Maturity Securities [Line Items]          
Conversion of stock, shares converted | shares 9,137        
Class C | Visa Stock Exchange [Member]          
Schedule Of Held To Maturity Securities [Line Items]          
Conversion of stock, shares converted | shares 3,045        
Securities Concentration Risk [Member] | Stockholders' Equity, Total [Member] | Other Than U.S. Government and Agencies [Member]          
Schedule Of Held To Maturity Securities [Line Items]          
Concentration Risk, Percentage     10.00%   10.00%