Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018
Significant Accounting Policies [Line Items]
Retained earnings		$ 3,791,838				$ 2,866,837				$ 3,791,838		$ 2,866,837				$ 2,861,035
Net income available to common stockholders		266,264	$ 274,817	$ 237,798	$ 194,961	117,210	$ 148,620	$ 123,193	$ 101,483	973,840	[1]	490,506	[1]	$ 382,685
Forecast
Significant Accounting Policies [Line Items]
Expected right-of-use assets upon adoption of new accounting standard															$ 150,000
Accounting Standards Update 2014-09
Significant Accounting Policies [Line Items]
Retained earnings						(5,802)						(5,802)
Cumulative adjustment for new accounting standards	[2]					(5,802)						(5,802)
Accounting Standards Update 2014-09 | Effect of Change Higher/(Lower)
Significant Accounting Policies [Line Items]
Retained earnings		$ (7,417)								(7,417)
Net income available to common stockholders										$ (1,615)
Accounting Standards Update 2016-01
Significant Accounting Policies [Line Items]
Cumulative adjustment for new accounting standards	[2]					$ 74,595						$ 74,595
Non-marketable securities | Other investments | Equity method investee | SPD Silicon Valley Bank Co., Ltd.
Significant Accounting Policies [Line Items]
Ownership interest percentage										50.00%
Lower Limit
Significant Accounting Policies [Line Items]
Duration of the sale restrictions										3 months
Derivative, Term of Contract										1 year
Lower Limit | Non-marketable securities | Consolidated venture capital and private equity fund investments | Equity method investee
Significant Accounting Policies [Line Items]
Ownership interest percentage										20.00%
Lower Limit | Non-marketable securities | Investments in limited partnerships | Equity method investee
Significant Accounting Policies [Line Items]
Ownership interest percentage										5.00%
Upper Limit
Significant Accounting Policies [Line Items]
Duration of the sale restrictions										6 months
Ownership interest percentage										5.00%		5.00%
Derivative, Term of Contract										5 years

[1] Included in income tax expense, net income available to common stockholders, earnings per common share-basic and earnings for common share-diluted, for the years ended December 31, 2018 and 2017, are tax benefits recognized associated with the adoption of Accounting Standards Update ("ASU") 2016-09, Improvements to Employee Share-Based Payment Accounting in the first quarter of 2017. This guidance was adopted on a prospective basis with no change to prior period amounts.

[2] See Note 2- "Summary of Significant Accounting Policies" of the "Notes to Consolidated Financial Statements" under Part II, Item 8 of this report for additional details.