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Fair Value Measurements - Summary of Carrying Values and Corresponding Fair Values for Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
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Fair Value Of Financial Instruments [Line Items] |  |
Fixed maturity securities-held-to-maturity | $ 576,989 | $ 627,349
Fixed maturity securities-held-to-maturity | 550,153 | 583,287
Fixed maturity securities-available-for-sale | 202,701 | 149,139
Equity securities | 12,260 | 6,766
Carrying Amount [Member] |  |
Fair Value Of Financial Instruments [Line Items] |  |
Fixed maturity securities-held-to-maturity | 550,153 | 583,287
Fixed maturity securities-available-for-sale | 202,701 | 149,139
Equity securities | 12,260 | 6,766
Cash and cash equivalents | 116,778 | 92,676
Short-term Investments | 86,131 | 68,924
Other Investments | 10,271 |
Fair Value [Member] |  |
Fair Value Of Financial Instruments [Line Items] |  |
Fixed maturity securities-held-to-maturity | 576,989 | 627,349
Fixed maturity securities-available-for-sale | 202,701 | 149,139
Equity securities | 12,260 | 6,766
Cash and cash equivalents | 116,778 | 92,676
Short-term Investments | 86,131 | 68,924
Other Investments | $ 10,271 |

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- Definition Amount of debt securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -Subparagraph (b)-(g) -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803 + Details
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- Definition Amount of equity securities categorized neither as held-to-maturity nor as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803 + Details
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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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- Definition Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.6) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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