Statutory Information - Summary of Amounts Disclosed Under Statutory Accounting Practices (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Statutory Capital [Abstract]
Statutory net income	$ 72,714	$ 54,612
Statutory policyholders' surplus	711,990	992,075
Contingency loss reserves	$ 5,333,024	$ 4,803,752

An amount of money established from retained earnings to allow for unforeseen losses in business. Amount of reserves for future policy claims payable and loss expenses to be incurred.

No definition available.

+ Details

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Namespace Prefix:	mtg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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- Definition

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(23)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479989/944-505-50-1

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators.

+ References

+ Details

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