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Investments - Additional Information (Detail) - 6 months ended Jun. 30, 2015 - USD ($)
$ in Thousands
Total
Schedule of Available-for-sale Securities [Line Items]  
Unrealized net (losses) gains on available-for-sale securities $ 182
Municipal Securities [Member]  
Schedule of Available-for-sale Securities [Line Items]  
Maturity period of investments One year or less