Equity-Based Compensation - SARs Additional Information (Detail) - SARs - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of SARs exercisable (in shares)	287,219	456,082
SARs exercisable weighted average price (in dollars per share)	$ 11.28	$ 10.69
Number of SARs expected to vest (in shares)	19,356
Aggregate intrinsic value of SARs outstanding	$ 1,236	$ 1,100