Taxes - Changes in the Reserve for Income Taxes, Excluding Interest and Penalties (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance of reserve for income taxes	$ 6,749	$ 5,719
Gross amounts of decreases in unrecognized tax benefits as a result of tax positions taken in prior periods		(56)
Gross amounts of increases in unrecognized tax benefits as a result of tax positions taken in prior periods	69
Gross amounts of increases in unrecognized tax benefits as a result of tax positions taken in the current period	1,499	1,993
Gross amounts of decreases in unrecognized tax benefits relating to settlements with taxing authorities		(116)
Gross amounts of decreases in unrecognized tax benefits as a result of the expiration of the applicable statutes of limitations	(1,023)	(791)
Balance of reserve for income taxes	$ 7,294	$ 6,749

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

No definition available.

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Amount of unrecognized tax benefits.

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