Reinsurance - Effect of Reinsurance on Premiums Earned, Benefits Incurred and Reserve Changes (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Insurance Premiums:
Direct	$ 63.2us-gaap_DirectPremiumsEarned	$ 67.7us-gaap_DirectPremiumsEarned
Assumed	8.8us-gaap_AssumedPremiumsEarned	9.3us-gaap_AssumedPremiumsEarned
Ceded	(60.3)us-gaap_CededPremiumsEarned	(63.1)us-gaap_CededPremiumsEarned
Net	11.7us-gaap_PremiumsEarnedNetLife	13.9us-gaap_PremiumsEarnedNetLife
Benefits and Other Changes in Insurance Policy Reserves:
Direct	304.2	296.4
Assumed	10.0	5.4
Ceded	(72.7)	(67.1)
Net	$ 241.5	$ 234.7

Amount of earned premiums assumed from other entities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Amount of earned premiums ceded to other entities.

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- Definition

Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 2

-Subparagraph (SX 210.12-17)

-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.1)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Amount, before effect of policies assumed or ceded, of expense related to provision for policy benefits and costs incurred.

+ References

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Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.

+ References

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of life premiums earned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Amount of policy benefits and costs incurred for policies assumed.

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Amount of reduction of provision for policy benefits and costs incurred for policies ceded.

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