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Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2013
Income Taxes [Line Items]        
Corporate tax rate of the company 0.00% 0.00% 0.00%  
Net increase (decrease) in valuation allowances $ (15,295) $ (16,042)    
Tax credits, net capital and operating loss carryforwards 773,721 451,247    
Tax credits, net capital and operating loss carryforwards having expiration date $ 214,538 98,912    
Tax credits, net capital and operating loss carryforwards expiration date Through 2036 for $214,538 in net operating losses      
Gross unrecognized tax benefits $ 196,668 126,706 $ 123,942 $ 130,371
Accrued income taxes payable for interest and penalties relating to unrecognized tax benefits 31,138 22,219    
Accrued income taxes payable recognized in the statements of income 8,919 $ 1,364    
Expected decrease in unrecognized tax benefits within next 12 months $ 28,066      
September 30, 2014 [Member]        
Income Taxes [Line Items]        
Tax credits, net capital and operating loss carryforwards expiration date Through 2035 for $98,912 in net operating losses