This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a),(c)-(e)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563

Name:	us-gaap_MarketableSecuritiesGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Marketable Securities and Certificates of Deposit - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule Of Marketable Securities [Line Items]
Certificates of Deposit, at Carrying Value			$ 63,527
Securities Investments - Debt Securities [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized Gains (Losses)	$ (13)	$ (13)
Securities Investments - Equity Securities [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized and Unrealized Gains (Losses)	(11)	(96)
Debt Securities Carried by EGL [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized and Unrealized Gains (Losses)	101	(147)
Investment Funds [Member]
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Realized and Unrealized Gains (Losses)	$ (188)	$ 1,062