Quarterly report pursuant to Section 13 or 15(d)

Debt (Details)

v3.8.0.1
Debt (Details)
6 Months Ended
Mar. 31, 2018
USD ($)
letter_of_credit
Mar. 31, 2017
USD ($)
Credit Agreement Expiring 2022    
Debt Instrument [Line Items]    
Dividend payment restriction ratio (less than) 2.5  
Total leverage ratio (less than) 1.0  
Interest paid $ 100,000 $ 1,600,000
Letters of Credit    
Debt Instrument [Line Items]    
Number of letters of credit issued | letter_of_credit 3  
Outstanding borrowings $ 2,700,000  
Letters of Credit (Other than Revolving Credit Agreement)    
Debt Instrument [Line Items]    
Number of letters of credit issued | letter_of_credit 2  
Outstanding borrowings $ 3,000,000  
Line of Credit | Credit Agreement Expiring 2022 | Revolving Credit Facility    
Debt Instrument [Line Items]    
Maximum borrowing capacity 400,000,000  
Line of Credit | Credit Agreement Expiring 2022 | Bridge Loan    
Debt Instrument [Line Items]    
Maximum borrowing capacity 5,000,000  
Line of Credit | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 50,000,000  
Minimum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Commitment fee percentage 0.125%  
Maximum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Commitment fee percentage 0.275%  
Base Rate | Minimum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Basis spread on variable rate 0.00%  
Base Rate | Maximum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Basis spread on variable rate 0.75%  
Eurocurrency Rate | Minimum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Basis spread on variable rate 1.00%  
Eurocurrency Rate | Maximum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Basis spread on variable rate 1.75%  
Index Rate | Minimum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Basis spread on variable rate 1.00%  
Index Rate | Maximum | Credit Agreement Expiring 2022 | Letters of Credit    
Debt Instrument [Line Items]    
Basis spread on variable rate 1.75%