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Fair Value Measurements - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Unrealized loss on debt securities $ 1,744 $ 3,348
Other-than-temporary impairment on debt securities 2,727  
Accumulated temporary impairment 2,400  
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Fair value of debt security 12,220 $ 12,658
Unrealized loss on debt securities $ 1,744