Basis of Presentation Recent Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			9 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Noninterest income		$ 158,778	$ 144,140	$ 404,965	$ 343,050
Operating Leases, Future Minimum Payments Due						$ 217,000
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 1,300		$ 14,400
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Diluted Earnings Per Share		$ 0.02		$ 0.27
Venture capital and private equity fund investments | Fair value accounting
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-marketable securities, cost method accounting		$ 206,500		$ 206,500		221,700
Venture capital and private equity fund investments | Cost method accounting
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Non-marketable securities, cost method accounting		$ 102,956		$ 102,956		$ 114,606
Lower Limit | Scenario, Forecast | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax (Less than)	$ 7,000
Noninterest income	10,000
Lower Limit | Scenario, Forecast | 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)	110,000
Upper Limit | Scenario, Forecast | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax (Less than)	10,000
Noninterest income	15,000
Upper Limit | Scenario, Forecast | 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)	$ 120,000