Marketable Securities and Certificates of Deposit - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Marketable Securities [Line Items]
Certificates of Deposit, at Carrying Value	$ 100,000	$ 63,527
Securities Investments - Debt Securities [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized Gains (Losses)	(28)	(38)	$ (46)
Securities Investments - Equity Securities [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized and Unrealized Gains (Losses)	(193)	64	(1,403)
Debt Securities Carried by EGL [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized and Unrealized Gains (Losses)	546	(865)	(937)
Investment Funds [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized and Unrealized Gains (Losses)	$ (5,113)	$ 4,088	$ 2,128