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Recent Accounting Pronouncements - Additional Information (Detail) - USD ($)
Sep. 30, 2020
Oct. 01, 2019
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]          
Cumulative-effect adjustment to retained earnings $ 457,859,000   $ 425,868,000 $ 374,467,000 $ 222,224,000
Cumulative Effect Period Of Adoption Adjustment [Member]          
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]          
Cumulative-effect adjustment to retained earnings       $ (1,239,000)  
Accounting Standards Update 2016-02 [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]          
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]          
Cumulative-effect adjustment to retained earnings   $ 0