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
Mar. 31, 2014	Mar. 31, 2013
Accounting Policies [Abstract]
Net income	$ 74,820	$ 72,270
Depreciation	5,584	5,704
Amortization	9,214	8,242
Equity in earnings of unconsolidated affiliates	(31,891)	(27,588)
Distributions received from unconsolidated affiliate	31,505	27,821
Stock-based compensation	2,823	5,293
Provision for losses on receivables	(25)	216
Deferred income tax expense	4,686	(7,730)
Gain on sale of SEI AK	(5,582)	(22,112)
Net gain from investments	(136)	(280)
Change in other long-term liabilities	705	368
Change in other assets	(3,273)	2,832
Other	(1,901)	(7,996)
Decrease (increase) in Restricted cash for broker-dealer operations	0	500
Decrease (increase) in Receivables from regulated investment companies	(3,908)	(5,473)
Decrease (increase) in Receivables	(15,453)	(9,127)
Decrease (increase) in Other current assets	(3,266)	(2,466)
Increase (decrease) in Accounts payable	(7,862)	(4,618)
Increase (decrease) in Accrued liabilities	(12,199)	4,571
Increase (decrease) in Deferred revenue	101	(952)
Total adjustments	(30,878)	(32,795)
Net cash provided by operating activities	$ 43,942	$ 39,475

Name:	us-gaap_AccountingPoliciesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The sum of adjustments which are added to or deducted from net income or loss, including the portion attributable to noncontrolling interest, to reflect cash provided by or used in operating activities, in accordance with the indirect cash flow method.