Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($) Integer	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Operating Segments \| Integer	3
Ceded Policy Loans	$ 3,206.1	$ 3,150.1
Accumulated Depreciation for Property and Equipment	989.4	902.6
Value of Business Acquired	31.9	24.0
Accumulated Amortization of Value of Business Acquired	119.2	133.1
Amortization of Value of Business Acquired	5.1	4.6	$ 3.5
Deferred Gain on Reinsurance	23.8	31.9
Premium tax expense	152.5	146.5	$ 139.2
Participation Fund Account Assets (PFA)	$ 331.1	$ 338.8

Seperate fund for mutual policies in-force.

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- Definition

Loans ceded to reinsurers. These loans use insurance policy funds such as cash surrender values as collateral.

+ References

No definition available.

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- Definition

Taxes incurred for premium written during the period.

+ References

No definition available.

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- Definition

Accumulated amortization of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs, deferred acquisition costs of insurance companies, or deferred leasing costs for real estate operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
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- Definition

Total carrying amount of consideration received or receivable as of the balance sheet date representing potential earnings that were not as yet recognized as revenue or other forms of income in conformity with GAAP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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- Definition

Amount of the present value of future profits asset amortized.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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The remaining unamortized carrying amount as of the balance sheet date of expected future earnings from insurance contracts acquired (also known as present value of future profits).

+ References

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