Summary Of Significant Accounting Policies (Adjustments To Reconcile Net Income To Net Cash Provided By Operating Activities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Accounting Policies [Abstract]
Net income	$ 49,739	$ 54,113	$ 99,974	$ 112,153
Depreciation	5,630	5,391	11,062	11,002
Amortization	7,407	6,792	15,029	13,023
Equity in earnings of unconsolidated affiliate	(22,712)	(29,530)	(50,042)	(58,479)
Distributions received from unconsolidated affiliate			47,443	50,760
Stock-based compensation	3,865	3,810	7,898	7,542
Provision for Doubtful Accounts			(104)	(327)
Deferred income tax expense			(1,291)	(36)
Net realized gains from investments			(3,869)	(5,330)
Change in other long-term liabilities			2,356	1,904
Change in other assets			(916)	(1,658)
Other			657	3,858
Decrease (increase) in receivables from regulated investment companies			(7,881)	(1,953)
Decrease (increase) in Receivables			(26,992)	(15,353)
Decrease (increase) in Other current assets			147	(211)
Increase (decrease) in Accounts payable			1,851	(1,727)
Increase (decrease) in Accrued liabilities			(18,810)	(21,081)
Increase (decrease) in Deferred revenue			(1,399)	(1,247)
Total adjustments			(24,861)	(19,313)
Net cash provided by operating activities			$ 75,113	$ 92,840