Derivative financial instruments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Breakdown of fair value amount of derivative financial instruments [Abstract]
Loss on cash flow hedges	$ 17,335	$ 16,960
Interest Rate Derivatives [Member] \| Cash Flow Hedge [Member]
Breakdown of fair value amount of derivative financial instruments [Abstract]
Assets	10,983		$ 8,230
Liabilities	320,366		329,731
Loss on cash flow hedges	(17,335)	(16,960)
Gain (loss) on net amount of time value component	(336)	$ (274)
After-tax result accumulated in equity	$ 96,141		$ 80,968

No definition available.

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- Definition

The gain (loss) on the change in fair value of the hedged item used as a basis for recognising hedge ineffectiveness. Hedge ineffectiveness is the extent to which the changes in the fair value or the cash flows of the hedging instrument are greater or less than those on the hedged item.

+ References

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- Definition

The gains (losses) recognised in other comprehensive income on cash flow hedges, before tax. [Refer: Cash flow hedges [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The amount of a hedging instrument, recognised as an asset. [Refer: Hedging instruments [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of a hedging instrument, recognised as a liability. [Refer: Hedging instruments [member]]

+ References

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- Definition

A component of equity representing the reserve of cash flow hedges in relation to continuing hedges. [Refer: Reserve of cash flow hedges]

+ References

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