Basis of Presentation Recent Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fund Management Fees	$ 5,736	$ 5,169
Income tax expense	73,966	51,405
Accounts Receivable, Gross, Current	47,978		$ 21,606	$ 55,946
Deferred fees	734		736	27,057
Taxes Payable, Current	67,001		2,458	4,675
Noninterest income	155,518	117,659
Operating Leases, Future Minimum Payments Due				226,000
Retained earnings	3,160,081		$ 2,861,035	$ 2,866,837
Net income available to common stockholders	$ 194,961	$ 101,483
Diluted (dollars per share)	$ 3.63	$ 1.91
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax (Less than)	$ 300
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fund Management Fees	(870)
Income tax expense	(239)
Accounts Receivable, Gross, Current	(37,099)
Deferred fees	(27,951)
Taxes Payable, Current	1,978
Retained earnings	(6,433)
Net income available to common stockholders	$ (631)
Diluted (dollars per share)	$ (0.01)
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax (Less than)	$ (5,802)
Adjustments for New Accounting Principle, Early Adoption [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fund Management Fees	6,606
Income tax expense	74,205
Accounts Receivable, Gross, Current	85,077
Deferred fees	28,685
Taxes Payable, Current	65,023
Retained earnings	3,166,514
Net income available to common stockholders	$ 195,592
Diluted (dollars per share)	$ 3.64
Non-marketable securities | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax (Less than)	$ 74,600
Equity securities | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax (Less than)	29,200
Other Assets [Member] | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(34,340)
Deferred Revenue [Domain] | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(26,321)
Other liability | Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ (2,217)