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New Accounting Pronouncements - Additional Information (Detail) - USD ($)
 3 Months Ended 12 Months Ended
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2016
Sep. 30, 2015
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]            
Reclassification of current deferred tax assets to noncurrent deferred tax assets $ 21,075,000       $ 21,075,000 $ 27,517,000
Increase in deferred tax assets and retained earnings         5,197,000  
Payments for tax withholdings for equity awards previously recorded in operating activities         80,000 541,000
New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2015-17 [Member]            
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]            
Reclassification of current deferred tax assets to noncurrent deferred tax assets           9,300,000
New Accounting Pronouncement, Early Adoption, Effect [Member] | Accounting Standards Update 2016-09 [Member]            
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]            
Increase in deferred tax assets and retained earnings         $ 5,200,000  
Income tax benefit $ 633,000   $ 67,000      
Additional income tax expense   $ 242,000   $ 201,000    
Payments for tax withholdings for equity awards previously recorded in operating activities           $ 541,000