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Dividends and Equity Issuance Program - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Jun. 30, 2020
Dividends and Equity Issuance [Line Items]      
Dividends declared and paid $ 9,704,000 $ 9,564,000  
Declared and paid dividends, per share $ 0.70 $ 0.695  
At-The-Market Equity Issuance Program (ATM)      
Dividends and Equity Issuance [Line Items]      
Aggregate sales of threshold amount     $ 100,000,000
Share issued 0   2,704
Average sale price per share     $ 101.30
Net cash proceeds from stock issued     $ 270,000
Payment of stock issuance cost     $ 4,000
At-The-Market Equity Issuance Program (ATM) | Other Expenses      
Dividends and Equity Issuance [Line Items]      
Payments for stock issuance $ 508,000