Income Taxes - Narrative and Unrecognised Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Increase (decrease) in valuation allowance	$ (66,500)	$ 2,200	$ 14,600
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Balance at beginning of period	22,395	18,022
Additions related to prior periods tax positions	726	2,098
Reductions related to prior periods tax positions	(82)
Additions related to current period tax positions	1,835	2,466
Reductions due to lapse of applicable statute of limitations	(557)	(130)
Currency translation adjustment	(66)	(61)
Balance at end of period	24,251	22,395	18,022
Interest and penalties as a component of income tax expense	$ 200	$ 100	$ 300

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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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Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from foreign currency translation.

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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 expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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

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Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

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