Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of total amounts of unrecognized tax benefits
Unrecognized Tax Benefits, Beginning Balance	$ 9,218	$ 6,794
Reductions of tax positions taken during previous years	(806)	(304)
Additions based on uncertain tax positions related to the current period	2,590	2,085
Additions based on uncertain tax positions related to prior periods	43	675
Cumulative translation adjustment	(34)	(32)
Unrecognized Tax Benefits, Ending Balance	11,011	9,218	$ 6,794
Unrecognized tax benefit netted against deferred tax assets	10,590	8,678
Unrecognized tax benefits, if recognized, would impact effective tax rate	421
Amount of liability for uncertain tax positions that could decrease within the next twelve months	126
Accrued interest and penalty expense related to estimated obligations for unrecognized tax benefits	294	375
Accrued interest and penalty expense related to estimated obligations for unrecognized tax benefits, amount recognized	128	$ 78	$ 86
Release of provision on uncertain tax positions due to the expiration of certain statutes of limitation in foreign jurisdictions	$ 184