Quarterly report pursuant to Section 13 or 15(d)

Equity - Schedule of Company's Outstanding Shares of Common Stock and Treasury Shares (Detail)

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Equity - Schedule of Company's Outstanding Shares of Common Stock and Treasury Shares (Detail)
$ in Thousands
 6 Months Ended
Mar. 31, 2018
USD ($)
shares
Schedule Of Stockholders Equity [Line Items]  
Beginning balance, shares 41,691,541
Ending balance, shares 41,817,541
Treasury shares outstanding, Beginning balance (3,296,034)
Treasury shares outstanding, Ending balance (3,170,034)
Treasury shares cost, Beginning balance | $ $ (11,983)
Issuance of treasury shares | $ 5
Treasury shares cost, Ending balance | $ $ (11,525)
Treasury Stock [Member]  
Schedule Of Stockholders Equity [Line Items]  
Issuance of treasury shares 126,000
Issuance of treasury shares | $ $ 458
Common Stock [Member]  
Schedule Of Stockholders Equity [Line Items]  
Beginning balance, shares 44,987,574
Issuance of treasury shares 126,000
Ending balance, shares 44,987,574