Income taxes (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 86,180
Additions based on tax positions related to the current year	3,781
Additions for tax positions of prior years	2,761
Reductions for tax positions of prior years	(25,348)
Settlements	(277)
Reductions due to lapse of statutes of limitations	(21,178)
Ending balance	$ 45,919

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The gross amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns as of the balance sheet date.

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The gross amount of decreases in unrecognized tax benefits resulting from tax positions taken in prior period tax returns, excluding amounts pertaining to examined tax returns.

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The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities.

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The gross amount of increases in unrecognized tax benefits resulting from tax positions that have been or will be taken in the tax return for the current period, excluding amounts pertaining to examined tax returns.

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