Income taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at	$ 86,180
Additions based on tax positions related to the current year	1,890
Reductions for tax positions of prior years	(15,508)
Settlements	(277)
Reductions due to lapse of statutes of limitations	(14,404)
Balance at	$ 57,881

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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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