Business Segment and Foreign Operations - Long-lived Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-Lived Assets [Line Items]
Total long-lived tangible assets	$ 115,528	$ 110,247
United States
Long-Lived Assets [Line Items]
Total long-lived tangible assets	14,674	11,948
People's Republic of China (PRC)
Long-Lived Assets [Line Items]
Total long-lived tangible assets	96,984	94,113
Other
Long-Lived Assets [Line Items]
Total long-lived tangible assets	$ 3,870	$ 4,186