Segment Reporting - Long Lived Assets Attributed to Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	$ 130,745	$ 107,076	$ 100,701
United States
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	61,557	54,703	54,157
Americas-Other
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	10,702	13,834	13,486
Germany
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	30,154	26,611	23,734
Europe-Other
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	24,935	9,124	6,949
Japan
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	1,039	558	460
Asia-Other
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	$ 2,358	$ 2,246	$ 1,915