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Investments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2013 | Jun. 30, 2013 | Dec. 31, 2012
Investment [Line Items] |  |  |
Amount of investments, available for sale |  |  | $ 0
Net unrealized loss on available-for-sale securities, net of tax effect | (3) | (11) |
Municipal Securities [Member] |  |  |
Investment [Line Items] |  |  |
Amount of investments, available for sale | $ 48,439 | $ 48,439 |
Maturity period of investments |  | One year or less |

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- Definition Amount of investment in debt and equity 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 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: 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 + Details
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- Definition Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=28358780&loc=SL7669646-108580 + Details
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