Reinsurance - Quota Share Agreement Terms (Details)		12 Months Ended
Reinsurance - Quota Share Agreement Terms (Details)	Dec. 31, 2025	Dec. 31, 2025
2020 QSR and 2021 QSR - 2021 NIW
Effects of Reinsurance [Line Items]
Quota Share %		14.80%
Annual Loss Ratio to Exhaust Profit Commission		69.00%
Optional Reduced Quota Share %, option 1		12.30%
Optional Reduced Quota Share %, option 2		10.00%
2021 QSR and 2022 QSR - 2021 NIW
Effects of Reinsurance [Line Items]
Quota Share %		11.10%
Annual Loss Ratio to Exhaust Profit Commission		69.00%
Optional Reduced Quota Share %, option 1		9.40%
Optional Reduced Quota Share %, option 2		7.00%
2021 QSR and 2022 QSR - 2022 NIW
Effects of Reinsurance [Line Items]
Quota Share %	13.80%	15.00%
Annual Loss Ratio to Exhaust Profit Commission	67.50%	57.50%
Optional Reduced Quota Share %, option 1		11.50%
Optional Reduced Quota Share %, option 2		9.20%
2022 QSR and 2023 QSR - 2022 NIW
Effects of Reinsurance [Line Items]
Quota Share %	14.50%	15.00%
Annual Loss Ratio to Exhaust Profit Commission	67.50%	62.00%
Optional Reduced Quota Share %, option 1		12.10%
Optional Reduced Quota Share %, option 2		9.70%
2022 QSR and 2023 QSR - 2023 NIW
Effects of Reinsurance [Line Items]
Quota Share %		15.00%
Annual Loss Ratio to Exhaust Profit Commission		62.00%
Optional Reduced Quota Share %, option 1		12.50%
Optional Reduced Quota Share %, option 2		10.00%
QSR 2023 - 2023 NIW
Effects of Reinsurance [Line Items]
Quota Share %		10.00%
Annual Loss Ratio to Exhaust Profit Commission		58.50%
Optional Reduced Quota Share %, option 1		8.00%
Optional Reduced Quota Share %, option 2		7.00%
QSR 2024 - 2024 NIW
Effects of Reinsurance [Line Items]
Quota Share %		30.00%
Annual Loss Ratio to Exhaust Profit Commission		56.00%
Optional Reduced Quota Share %, option 1		23.00%
Optional Reduced Quota Share %, option 2		15.00%
QSR 2025 - 2025 NIW
Effects of Reinsurance [Line Items]
Quota Share %		40.00%
Annual Loss Ratio to Exhaust Profit Commission		63.00%
Optional Reduced Quota Share %, option 1		30.00%
Optional Reduced Quota Share %, option 2		20.00%
Credit Union QSR Transaction
Effects of Reinsurance [Line Items]
Quota Share %		65.00%
Annual Loss Ratio to Exhaust Profit Commission		50.00%

MGIC INVESTMENT CORP 10-K