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Employee Stock Purchase Plan - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Feb. 29, 2012
Sep. 30, 2015
Sep. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Percentage not exceeding to periodic payment of purchase price   10.00%  
Common stock, shares issued   25,562,994 25,002,807
Stock Purchase Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Additional Common Shares Authorized 500,000    
Additional Common Shares Authorized   1,000,000  
Stock Purchase Plan, requisite continuous service   1 year  
Annual offerings description   implementation of up to 10 annual offerings beginning on the first day of October starting in 2008, with each offering terminating on September 30 of the following year.  
Closing price of common stock on the first and last day of the offering   85.00%  
Maximum common stock value purchased by participant annually   $ 25,000  
Common stock, shares issued   702,689  
1998 Employee Stock Purchase Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Additional Common Shares Authorized   52,837