Restricted net assetS (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted net assets in the Company's consolidated subsidiaries	$ 21,096	$ 20,932
Consolidated net assets	160,200	160,200
Cash restricted in China as a result of ongoing litigation and unfulfilled government grants
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted net assets in the Company's consolidated subsidiaries	10,936	11,018
China earnings restricted to fund statutory common reserves in China
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted net assets in the Company's consolidated subsidiaries	9,240	9,005
Loan agreements in Japan requiring local subsidiaries to maintain minimum net asset levels
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted net assets in the Company's consolidated subsidiaries	$ 920	$ 909