Debt and obligations under capital lease - Long-term debt and obligations under capital lease (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument
Loans from banks and other parties collateralized by tangible and intangible personal property and real estate with a maturity of two to six years (2017 - 20 months to seven years), with a weighted average interest rate of 4.41% (2017 - 4.11%)	$ 773,548	$ 724,208
Obligations under capital lease	68	22
Total long-term debt and obligations under capital leases	773,616	724,230
Less: Current portion	6,332	6,407
Less: Discount on secured term loan	2,642	3,092
Less: Debt issuance costs	10,996	13,979
Non-current portion of long-term debt and obligations under capital lease	$ 753,646	$ 700,752
Weighted average interest rate	4.41%	4.11%
Minimum
Debt Instrument
Period of debt repayment	2 years	20 months
Maximum
Debt Instrument
Period of debt repayment	6 years	7 years

Long-term Debt and Capital Lease Obligations Including Current Maturities, Period of Repayment

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- Definition

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Amount, after accumulated amortization, of debt discount.

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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- Definition

Weighted average interest rate of debt outstanding.

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- Definition

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

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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