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Financing Arrangements - Underwritten Public Offering (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 6 Months Ended
Dec. 31, 2018
Mar. 31, 2019
Mar. 31, 2020
Sep. 30, 2019
Financing Arrangements        
Stock issued under equity offering, net (in shares) 3,795,000 3,795,000    
Stock offering price (per share) $ 60.00      
Proceeds from equity offering, net $ 215,800 $ 215,832    
Underwriting discounts and commissions and offering expenses $ 11,900      
Self-insurance liabilities     $ 7,100 $ 7,400