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Comprehensive Income and Accumulated Other Comprehensive Income - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract] |  |
Comprehensive income | $ 10,321 | $ 14,476
Comprehensive income tax rate | 21.00% | 35.00%

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- Definition Other comprehensive income loss available for sale securities tax rate. + References No definition available. + Details
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- Definition Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e557-108580 + Details
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