Other Income, net - Summary of Other Income, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Nonoperating Income (Expense) [Abstract]
Interest and dividend income	$ 1,625	$ 1,673	$ 2,904
Gain on mutual fund investments	8,766	8,087	3,902
Change in fair value of earn-out consideration	0	4,060	0
Other, net	1,468	1,588	221
Other income, net	$ 11,859	$ 15,408	$ 7,027