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Marketable Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Sep. 30, 2016
Mar. 31, 2016
Marketable Securities [Abstract]      
Available-for-sale Securities, Gross Realized Gains $ (26)    
Available-for-sale Securities, Gross Realized Losses (6)    
Available-for-sale Securities, Gross Unrealized Gain $ 109    
Available-for-sale Securities, Gross Realized Gain (Loss)     $ 779
Investment Income, Amortization of Premium   $ 308