Major Categories of Interest and Similar Income, Net (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest and Other Income [Line Items]
Available-for-sale fixed-maturity securities	$ 3,552,896	$ 3,185,680	$ 3,210,655
Mortgage loans on real estate	377,917	367,196	367,506
Investment income on trading securities	11,645	9,735	4,624
Held-to-maturity fixed-maturity securities	15,894	26,781	38,618
Rental income on real estate		1,462us-gaap_RentalIncomeNonoperating	2,943us-gaap_RentalIncomeNonoperating
Interest on loans to affiliates	980us-gaap_InterestIncomeRelatedParty	1,549us-gaap_InterestIncomeRelatedParty	2,614us-gaap_InterestIncomeRelatedParty
Interest on acquired loans	27,548us-gaap_InterestAndFeeIncomeOtherLoans	27,817us-gaap_InterestAndFeeIncomeOtherLoans	31,085us-gaap_InterestAndFeeIncomeOtherLoans
Interest rate swaps	1,867us-gaap_InterestIncomeOther	697us-gaap_InterestIncomeOther	3,314us-gaap_InterestIncomeOther
Other invested assets	2,083us-gaap_OtherInterestAndDividendIncome	196us-gaap_OtherInterestAndDividendIncome	72us-gaap_OtherInterestAndDividendIncome
Policy loans	9,981	10,461	10,177
Short-term securities	7,864	5,575	4,872
Interest on assets held by reinsurers	2,798us-gaap_InsuranceInvestmentIncome	2,915us-gaap_InsuranceInvestmentIncome	3,043us-gaap_InsuranceInvestmentIncome
Total	4,011,473us-gaap_InterestAndOtherIncome	3,640,064us-gaap_InterestAndOtherIncome	3,679,523us-gaap_InterestAndOtherIncome
Less investment expenses	54,175	47,947	47,117
Total interest and similar income, net	$ 3,957,298	$ 3,592,117	$ 3,632,406

Interest and Fee Income, Policy Loans

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Investment income associated with the company's insurance services.

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities.

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Amount of operating interest income, including amortization and accretion of premiums and discounts, on held-to-maturity securities.

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Amount of other operating dividend and interest income, including amortization and accretion of premiums and discounts, on securities.

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Interest and fee income generated from consumer loans. Consumer loans are loans to individuals for household, family, and other personal expenditures. Such loans include residential mortgages, home equity lines-of-credit, automobiles and marine transport loans, credit card transactions, and others.

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Interest and fee income derived from loans not otherwise specified in the existing taxonomy.

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The amount of interest income and other income recognized during the period. Included in this element is interest derived from investments in debt securities, cash and cash equivalents, and other investments which reflect the time value of money or transactions in which the payments are for the use or forbearance of money and other income from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business).

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Amount of interest income earned from interest bearing assets not separately disclosed.

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Amount of interest income earned from interest-bearing assets owed to the entity by related party.

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Amount of expenses related to the generation of investment income.

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Includes all other interest income, net of discount accretion and premium amortization, and dividend income. It may include dividend income from equity securities that do not have readily determinable fair values that are reportable in Other Assets, and interest income on interest-only strips receivable (not in the form of a security) that are included in Other Assets.

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Income earned by providing the use of assets to an outside party in exchange for a payment or series of payments that is nonoperating in nature.

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This item represents the gain (loss) realized during the period from the sale of trading securities.

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