Business Segment and Foreign Operations - Long-Lived Tangible Assets by Geographic Area (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Long-lived Assets from External Customers and Long-Lived Assets [Line Items]
Long-lived tangible assets	$ 121,539	$ 115,528
United States
Long-lived Assets from External Customers and Long-Lived Assets [Line Items]
Long-lived tangible assets	15,399	14,674
People's Republic of China (PRC)
Long-lived Assets from External Customers and Long-Lived Assets [Line Items]
Long-lived tangible assets	101,960	96,984
All other countries
Long-lived Assets from External Customers and Long-Lived Assets [Line Items]
Long-lived tangible assets	$ 4,180	$ 3,870