Income Taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of unrecognized tax benefits, excluding penalties and interest
Balance at the beginning of the period	$ 6,843	$ 7,734	$ 8,448
Increases during the year:
Gross increases - tax positions in prior period	712	244	465
Gross increases - current-period tax positions	331	97	494
Decreases during the year:
Gross decreases - tax positions in prior period	(4,219)	(56)	(167)
Decreases due to settlements with taxing authorities	(1,385)	(178)	(21)
Decreases due to lapse of statute of limitations	(212)	(998)	(1,485)
Balance at the end of the period	$ 2,070	$ 6,843	$ 7,734
Number of open tax years settled			2 years

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of unrecognized tax benefits.

+ References

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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Represents the number of tax years settled, which were being audited in connection with the income tax examination.

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