Quarterly report pursuant to Section 13 or 15(d)

Repurchase of Common Stock (Details)

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Repurchase of Common Stock (Details) - USD ($)
 1 Months Ended 3 Months Ended 6 Months Ended
Mar. 31, 2018
Mar. 03, 2018
Feb. 03, 2018
Mar. 31, 2018
Mar. 31, 2018
Class of Stock [Line Items]          
Authorized amount $ 50,000,000     $ 50,000,000 $ 50,000,000
Aggregated number of shares repurchased (in shares) 3,113,545     3,113,545 3,113,545
Aggregated shares repurchased, value $ 43,200,000     $ 43,200,000 $ 43,200,000
Dollar value of shares that may yet be purchased under the plans 6,800,000     $ 6,800,000 6,800,000
Shares repurchased (in shares)       74,934  
Stock repurchased during period, value         1,500,000
Common Stock          
Class of Stock [Line Items]          
Dollar value of shares that may yet be purchased under the plans $ 6,800,000 $ 7,400,000 $ 7,800,000 $ 6,800,000 $ 6,800,000
Shares repurchased (in shares) 29,864 22,000 23,070 74,934  
Average price paid per share (usd per share) $ 19.12 $ 19.09 $ 20.46 $ 19.52  
Publicly Announced Plan | Common Stock          
Class of Stock [Line Items]          
Shares repurchased (in shares) 29,864 22,000 23,070 74,934