Long-Term Indebtedness (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Unamortized deferred financing fees	$ (1,379)	$ (1,774)
Long-term debt	635,937	630,789
Less current portion	(19,861)	(17,883)
Long-term debt, excluding current maturities	616,076	612,906
Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	286,140	266,214
Shelf Loan
Debt Instrument [Line Items]
Long-term debt, gross	50,000	50,000
Other
Debt Instrument [Line Items]
Long-term debt, gross	12,426	16,349
Medium-term Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 288,750	$ 300,000

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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