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Borrowing Limits Amounts Outstanding and Amounts Available under Revolving Credit Facility (Detail) - USD ($)
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2019
Debt Instrument [Line Items]      
Short-Term Borrowings Outstanding $ 71,600,000 $ 58,600,000 $ 65,800,000
Revolving Credit Facility      
Debt Instrument [Line Items]      
Revolving credit facility, limit 120,000,000.0 120,000,000.0 120,000,000.0
Short-Term Borrowings Outstanding 71,600,000 58,600,000 65,800,000
Letters of Credit Outstanding 100,000 100,000  
Available revolving credit facility $ 48,300,000 $ 61,300,000 $ 54,200,000