Amortized Cost and Estimated Fair Value of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost	$ 34,640	$ 80,390
Available-for-Sale, Gross Unrealized Gains	1,937	1,530
Available-for-Sale, Gross Unrealized Losses	32	632
Available-for-Sale, Fair Value	36,545	81,288
Debt Securities Carried by EGL
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost	13,522	47,583
Available-for-Sale, Gross Unrealized Gains	97	518
Available-for-Sale, Fair Value	13,619	48,101
Mutual Funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost	10,946	9,350
Available-for-Sale, Gross Unrealized Gains	412	191
Available-for-Sale, Gross Unrealized Losses	12	603
Available-for-Sale, Fair Value	11,346	8,938
Available-for-Sale
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost	10,172	23,457
Available-for-Sale, Gross Unrealized Gains	1,428	821
Available-for-Sale, Gross Unrealized Losses	20	29
Available-for-Sale, Fair Value	11,580	24,249
Available-for-Sale \| Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost		1,008
Available-for-Sale, Gross Unrealized Losses		2
Available-for-Sale, Fair Value		1,006
Available-for-Sale \| Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost		9,544
Available-for-Sale, Gross Unrealized Gains		9
Available-for-Sale, Fair Value		9,553
Available-for-Sale \| Other Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost		2,000
Available-for-Sale, Fair Value		2,000
Available-for-Sale \| Seed Capital Investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Cost	10,172	10,905
Available-for-Sale, Gross Unrealized Gains	1,428	812
Available-for-Sale, Gross Unrealized Losses	20	27
Available-for-Sale, Fair Value	$ 11,580	$ 11,690

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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