Marketable Securities Amortized Cost and Estimated Fair Value of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Total
Cost	$ 39,278	$ 34,640
Gross Unrealized Gains	1,851	1,937
Gross Unrealized Losses	86	32
Fair Value	41,043	36,545
Debt Securities Carried by EGL [Member]
Other Securities
Cost	20,335	13,522
Gross Unrealized Gains	61	97
Gross Unrealized Losses	2	0
Fair Value	20,394	13,619
Mutual Funds [Member]
Other Securities
Cost	7,765	10,946
Gross Unrealized Gains	1,198	412
Gross Unrealized Losses	75	12
Fair Value	8,888	11,346
Available-for-Sale [Member] | Securities Investments [Member]
Securities Investments
Cost	11,178	10,172
Gross Unrealized Gains	592	1,428
Gross Unrealized Losses	9	20
Fair Value	$ 11,761	$ 11,580