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Document and Entity Information
Aug. 06, 2020
Cover [Abstract]  
Entity Registrant Name MGIC INVESTMENT CORP
Amendment Flag false
Entity Central Index Key 0000876437
Document Type 8-K
Document Period End Date Aug. 06, 2020
Entity Incorporation State Country Code WI
Entity File Number 1-10816
Entity Tax Identification Number 39-1486475
Entity Address, Address Line One 250 East Kilbourn Avenue
Entity Address, City or Town Milwaukee
Entity Address, State or Province WI
Entity Address, Postal Zip Code 53202
City Area Code (414)
Local Phone Number 347-6480
Written Communications false
Soliciting Material false
Pre Commencement Tender Offer false
Pre Commencement Issuer Tender Offer false
Security 12b Title Common Stock
Trading Symbol MTG
Security Exchange Name NYSE
Entity Emerging Growth Company false