Summary of Significant Accounting Policies - Components of Other Non-Operating Income (Expense) Recognized in Condensed Consolidated Financial Statements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Nonoperating Income Expense [Abstract]
Interest Income	$ 938	$ 56
Foreign currency losses, net	(18)	(249)
Gain on sale of a private company investment	1,001	999
Other income (expense), net	58	(173)
Other non-operating income (expense), net	$ 1,979	$ 633