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Investments in Debt and Equity Securities - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Trading Securities And Other Trading Assets [Line Items]    
Available for sale investments gross pre-tax unrealized gain (loss) $ 3,701 $ 2,589
Proceeds from sale of investments available for sale 14,971 1,295
Pre tax reclassification of net investment realized gain (loss) into net income 690 618
Reclassification of net investment realized gain (loss) into net income, net of tax 423 377
Certificates of deposit, commercial paper and money market funds    
Schedule Of Trading Securities And Other Trading Assets [Line Items]    
Unrealized (losses) gains on investments, pre tax $ 1,802 $ (1,974)