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Supplementary Financial Data (Unaudited) - Selected Unaudited Consolidated Financial Results - Additional Information (Detail) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]                      
Amortization expense $ 1,400 $ 1,700 $ 1,700 $ 1,700 $ 1,700 $ 1,800 $ 1,800 $ 1,900 $ 12,709 [1] $ 13,982 [1] $ 13,673 [1]
[1] Cost of revenues and selling, general and administrative expenses exclude the amortization of intangible assets. See Note 7.