Other Income, net - Summary of Other Income, net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Income and Expenses [Abstract]
Interest and dividend income	$ 796	$ 308
Gain on sale and mark-to-market of mutual funds	3,526	3,133
Others, net	101	93
Other income, net	$ 4,423	$ 3,534