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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Nonoperating Income Expense [Abstract]
Interest Income	$ 776	$ 85	$ 1,714	$ 141
Foreign currency losses, net	(305)	(481)	(323)	(730)
Gain on sale of a private company investment	0	0	1,001	999
Other income (expense), net	104	114	162	(59)
Other non-operating income (expense), net	$ 575	$ (282)	$ 2,554	$ 351