Amortized Cost and Estimated Fair Value of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Cost	$ 32,113	$ 34,640
Marketable Securities, Gross Unrealized Gains	2,303	1,937
Marketable Securities, Gross Unrealized Losses	9	32
Marketable Securities, Fair Value	34,407	36,545
Debt Securities Carried by EGL
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Cost	13,937	13,522
Marketable Securities, Gross Unrealized Gains	92	97
Marketable Securities, Gross Unrealized Losses	3
Marketable Securities, Fair Value	14,026	13,619
Mutual Funds
Schedule Of Marketable Securities [Line Items]
Marketable Securities, Cost	7,708	10,946
Marketable Securities, Gross Unrealized Gains	766	412
Marketable Securities, Gross Unrealized Losses		12
Marketable Securities, Fair Value	8,474	11,346
Available-for-Sale \| Seed Capital Investments
Schedule Of Marketable Securities [Line Items]
Available-for-Sale, Cost	10,468	10,172
Available-for-Sale, Gross Unrealized Gains	1,445	1,428
Available-for-Sale, Gross Unrealized Losses	6	20
Available-for-Sale, Fair Value	$ 11,907	$ 11,580

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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