Long-term debt (Schedule of Long-term Debt Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Long-term debt
Senior unsecured bond	$ 119,100	$ 125,000
Secured long-term debt	423,749	405,120
Total long-term debt	542,849	530,120
Less: Deferred financing costs	(7,526)	(7,609)
Long-term debt, net of deferred financing costs	535,323	522,511
Less: Current portion of long-term debt, net of deferred financing, current	(49,428)	(91,495)
Long-term debt, excluding current maturities	$ 485,895	$ 431,016

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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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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

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