Income Taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of unrecognized tax benefits, excluding penalties and interest
Balance at the beginning of the period	$ 2,070	$ 6,843	$ 7,734
Increases during the year:
Gross increases - tax positions in prior period	345	712	244
Gross increases - current-period tax positions	44	331	97
Decreases during the year:
Gross decreases - tax positions in prior period	(135)	(4,219)	(56)
Decreases due to settlements with taxing authorities	(348)	(1,385)	(178)
Decreases due to lapse of statute of limitations	(358)	(212)	(998)
Balance at the end of the period	$ 1,618	$ 2,070	$ 6,843

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.

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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 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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