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Current Fair Value of Debt (Detail) - USD ($)
$ in Thousands

Mar. 31, 2018

Dec. 31, 2017

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Debt

$ 286,567

$ 294,713

Debt, fair value

292,963

302,718

7.75% Subordinated Notes due 2045

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Debt

^[1]

96,650

96,619

Debt, fair value

^[1]

99,770

100,059

7.875% Subordinated Notes due 2047

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Debt

^[2]

125,899

125,864

Debt, fair value

^[2]

129,175

130,429

Margin borrowing facilities

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Debt

64,018

72,230

Debt, fair value

$ 64,018

$ 72,230

[1]	As of March 31, 2018 and December 31, 2017, the carrying value and fair value of the 7.75% Subordinated Notes due 2045 are net of unamortized debt issuance cost of $3.4 million.
[2]	As of March 31, 2018 and December 31, 2017, the carrying value and fair value of the 7.875% Subordinated Notes due 2047 are net of unamortized debt issuance cost of $4.1 million.

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+ References

No definition available.

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

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