Debt and obligations under capital lease - Long-term debt and obligations under capital lease (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Debt Instrument
Loans from banks and other parties collateralized by tangible and intangible personal property and real estate with a maturity of 20 months to seven years (2016 - two to five years), with a weighted average interest rate of 4.11% (2016 - 4.27%)	$ 724,208	$ 602,083
Obligations under capital lease	22	19
Total long-term debt and obligations under capital leases	724,230	602,102
Less: Current portion	6,407	5,284
Less: Discount on secured term loan	3,092	1,515
Less: Debt issuance costs	13,979	9,535
Non-current portion of long-term debt and obligations under capital lease	$ 700,752	$ 585,768
Weighted average interest rate	4.11%	4.27%
Minimum
Debt Instrument
Period of debt repayment	20 months	2 years
Maximum
Debt Instrument
Period of debt repayment	7 years	5 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.

+ References

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-Publisher FASB
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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.

+ References

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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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No definition available.

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- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

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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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