XML 20 R1.htm IDEA: XBRL DOCUMENT v3.20.4
Document and Entity Information - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2020
Feb. 19, 2021
Jun. 30, 2020
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2020    
Document Transition Report false    
Entity File Number 1-10816    
Entity Registrant Name MGIC Investment Corp    
Entity Incorporation, State or Country Code WI    
Entity Tax Identification Number 39-1486475    
Entity Address, Address Line One 250 E. Kilbourn Avenue    
Entity Address, Postal Zip Code 53202    
Entity Address, City or Town Milwaukee,    
Entity Address, State or Province WI    
City Area Code (414)    
Local Phone Number 347-6480    
Title of 12(b) Security Common stock, par value $1 per share    
Trading Symbol MTG    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 2.8
Entity Common Stock, Shares Outstanding   338,779,666  
Documents Incorporated by Reference
The following documents have been incorporated by reference in this Form 10-K, as indicated:
DocumentPart and Item Number of Form 10-K Into Which Incorporated*
Proxy Statement for the 2021 Annual Meeting of Shareholders, provided such Proxy Statement is filed within 120 days after December 31, 2020. If not so filed, the information provided in Items 10 through 14 of Part III will be included in an amended Form 10-K filed within such 120 day period.Items 10 through 14 of Part III

* In each case, to the extent provided in the Items listed.
    
Entity Central Index Key 0000876437    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Amendment Flag false