Stockholders' Equity - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ 160,240	$ 194,451	$ 225,405	$ 211,656
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(6,897)	567
Unrealized loss on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	0	(1)
Defined benefit pension plan adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	229	168
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ (7,126)	$ 398	$ (8,401)	$ (1,723)