Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	$ 6,174,767	$ 5,677,508
Separate Account (variable annuity) assets	1,405,693	1,273,764
Financial Liabilities
Financial Liabilities
Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	5,782,052	5,421,832
Fair Value	5,782,052	5,421,832
Investments, Carrying Value	6,041,682	5,549,048
Investments, Fair Value	6,041,682	5,549,048
Separate Account (variable annuity) assets	1,405,693	1,273,764
Separate Account (variable annuity) assets, Fair Value	1,405,693	1,273,764
Short-term investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	167,903	100,442
Investments, Fair Value	167,903	100,442
Other investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	133,085	128,460
Investments, Fair Value	137,207	132,522
Other investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	52,516
Investments, Fair Value	52,516
Mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	626,897	603,812
Fair Value	626,897	603,812
Other [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	463,578	603,741
Fair Value	463,578	603,741
Municipal bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	1,559,209	1,413,118
Fair Value	1,559,209	1,413,118
Foreign government bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	56,973	49,624
Fair Value	56,973	49,624
Corporate bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	2,444,175	2,156,544
Fair Value	2,444,175	2,156,544
Other mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	631,220	594,993
Fair Value	631,220	594,993
Equity securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	39,211	26,774
Fair Value	39,211	26,774
Level 1 [Member]
Financial Liabilities
Financial Liabilities
Level 1 [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	38,671	89,930
Investments, Fair Value	232,169	196,895
Separate Account (variable annuity) assets, Fair Value	0
Level 1 [Member] \| Short-term investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Fair Value	167,903	97,929
Level 1 [Member] \| Other investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Fair Value
Level 1 [Member] \| Other investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 1 [Member] \| Mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 1 [Member] \| Other [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	25,841	64,444
Level 1 [Member] \| Municipal bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 1 [Member] \| Foreign government bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 1 [Member] \| Corporate bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	12,830	25,486
Level 1 [Member] \| Other mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 1 [Member] \| Equity securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	25,595	9,036
Level 2 [Member]
Financial Liabilities
Financial Liabilities
Level 2 [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	5,611,379	5,239,114
Investments, Fair Value	5,624,655	5,258,980
Separate Account (variable annuity) assets, Fair Value	1,405,693	1,273,764
Level 2 [Member] \| Short-term investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Investments, Fair Value		2,513
Level 2 [Member] \| Other investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Fair Value
Level 2 [Member] \| Other investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 2 [Member] \| Mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	626,897	603,812
Level 2 [Member] \| Other [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	437,737	539,297
Level 2 [Member] \| Municipal bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	1,546,912	1,413,118
Level 2 [Member] \| Foreign government bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	56,973	49,624
Level 2 [Member] \| Corporate bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	2,345,528	2,042,802
Level 2 [Member] \| Other mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	597,332	590,461
Level 2 [Member] \| Equity securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	13,276	17,353
Level 3 [Member]
Financial Liabilities
Financial Liabilities
Level 3 [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	132,002	92,788
Investments, Fair Value	184,858	93,173
Separate Account (variable annuity) assets, Fair Value
Level 3 [Member] \| Short-term investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 3 [Member] \| Other investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Fair Value	137,207	132,522
Level 3 [Member] \| Other investments [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Fair Value	52,516
Level 3 [Member] \| Mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 3 [Member] \| Other [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 3 [Member] \| Municipal bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	12,297
Level 3 [Member] \| Foreign government bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value
Level 3 [Member] \| Corporate bonds [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	85,817	88,256
Level 3 [Member] \| Other mortgage-backed securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	33,888	4,532
Level 3 [Member] \| Equity securities [Member] \| Recurring [Member]
U.S. government and federally sponsored agency obligations
Fair Value	$ 340	$ 385

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

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Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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+ Details

- 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 Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details

- Definition

+ References+ Details

- Definition

The fair value of the assets held by the Entity for the benefit of separate account policyholders.

+ References+ Details