Fair Value of Financial Instruments - Financial Instrument Not Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Level 1
Investments
Other investments	$ 0	$ 0
Deposit asset on reinsurance	0	0
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	0	0
Investment contract and policy reserves, account values on life contracts	0	0
Other policyholder funds	0	0
Short-term debt	0	0
Long-term debt	0	0
Level 2
Investments
Other investments	0	0
Deposit asset on reinsurance	0	0
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	0	0
Investment contract and policy reserves, account values on life contracts	0	0
Other policyholder funds	590,687	495,812
Short-term debt	0	0
Long-term debt	331,829	322,678
Level 3
Investments
Other investments	172,303	167,185
Deposit asset on reinsurance	2,925,672	2,634,012
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	4,720,941	4,609,880
Investment contract and policy reserves, account values on life contracts	102,290	98,332
Other policyholder funds	55,737	57,738
Short-term debt	135,000	135,000
Long-term debt	0	0
Carrying Amount
Investments
Other investments	168,500	163,312
Deposit asset on reinsurance	2,402,539	2,346,166
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	4,812,911	4,675,774
Investment contract and policy reserves, account values on life contracts	97,522	93,465
Other policyholder funds	646,424	553,550
Short-term debt	135,000	135,000
Long-term debt	302,247	298,025
Fair Value
Investments
Other investments	172,303	167,185
Deposit asset on reinsurance	2,925,672	2,634,012
Financial Liabilities
Investment contract and policy reserves, fixed annuity contracts	4,720,941	4,609,880
Investment contract and policy reserves, account values on life contracts	102,290	98,332
Other policyholder funds	646,424	553,550
Short-term debt	135,000	135,000
Long-term debt	$ 331,829	$ 322,678

Deposit Asset On Reinsurance Fair Value Disclosure

No definition available.

Name:	hmn_DepositAssetOnReinsuranceFairValueDisclosure
Namespace Prefix:	hmn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The fair value of accrued obligation to policyholders that relates to insured events under individual and group annuities and supplementary insurance contracts.

+ References

No definition available.

+ Details

Name:	hmn_LiabilityForFuturePolicyBenefitsIndividualAndGroupAnnuitiesAndSupplementaryContractsFairValue
Namespace Prefix:	hmn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Liability for policyholder account balances life fair value.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair Value of the liability as of the balance sheet date to the policyholders for funds held that are returnable under the terms of insurance contracts that were not separately reported.

+ References

No definition available.

+ Details

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- References

No definition available.

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- References

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of investments classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_OtherInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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