Annual report pursuant to Section 13 and 15(d)

Debt - Narrative (Details)

v3.10.0.1
Debt - Narrative (Details)
$ in Millions
12 Months Ended
Sep. 30, 2018
USD ($)
period
letter_of_credit
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2018
CAD ($)
period
letter_of_credit
Debt Instrument [Line Items]        
Interest expense $ 1,000,000 $ 2,162,000 $ 4,134,000  
Credit Agreement Expiring January 2020        
Debt Instrument [Line Items]        
Maximum borrowing capacity $ 400,000,000      
Leverage ratio 2.5      
Debt instrument, covenant consolidated leverage ratio actual 1      
Interest paid $ 600,000 $ 2,000,000 $ 3,700,000  
Credit Agreement Expiring January 2020 | Minimum | Base Rate        
Debt Instrument [Line Items]        
Margin (as a percent) 0.00%      
Credit Agreement Expiring January 2020 | Minimum | Eurocurrency Rate        
Debt Instrument [Line Items]        
Margin (as a percent) 1.00%      
Credit Agreement Expiring January 2020 | Minimum | Index Rate        
Debt Instrument [Line Items]        
Margin (as a percent) 1.00%      
Credit Agreement Expiring January 2020 | Maximum | Base Rate        
Debt Instrument [Line Items]        
Margin (as a percent) 0.75%      
Credit Agreement Expiring January 2020 | Maximum | Eurocurrency Rate        
Debt Instrument [Line Items]        
Margin (as a percent) 1.75%      
Credit Agreement Expiring January 2020 | Maximum | Index Rate        
Debt Instrument [Line Items]        
Margin (as a percent) 1.75%      
Swingline loans        
Debt Instrument [Line Items]        
Maximum borrowing capacity $ 5,000,000      
Letters of credit        
Debt Instrument [Line Items]        
Maximum borrowing capacity $ 50,000,000      
Number of letters of credit issued | letter_of_credit 2     2
Outstanding borrowings $ 700,000      
Letters of credit | Minimum        
Debt Instrument [Line Items]        
Leverage ratio to calculate annual commitment fee (as a percent) 0.125%      
Letters of credit | Maximum        
Debt Instrument [Line Items]        
Leverage ratio to calculate annual commitment fee (as a percent) 0.275%      
Atlantic Innovation Fund of Canada        
Debt Instrument [Line Items]        
Borrowings $ 500,000     $ 0.7
Interest expense $ 0      
Number of remaining quarterly installments | period 15     15
Letters of credit (Other than Revolving Credit Agreement)        
Debt Instrument [Line Items]        
Number of letters of credit issued | letter_of_credit 2     2
Outstanding borrowings $ 3,000,000