Investment Securities - Carrying Value and Ownership Percentage of Investments (Details) - Equity method accounting - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Consolidated venture capital and private equity fund investments
Investment Holdings [Line Items]
Nonmarketable securities	$ 148,096	$ 129,485
Consolidated venture capital and private equity fund investments | Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Nonmarketable securities	4,648	4,670
Consolidated venture capital and private equity fund investments | Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Nonmarketable securities	17,485	17,396
Consolidated venture capital and private equity fund investments | Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Nonmarketable securities	28,785	28,974
Consolidated venture capital and private equity fund investments | Strategic Investors Fund V funds
Investment Holdings [Line Items]
Nonmarketable securities	28,953	28,189
Consolidated venture capital and private equity fund investments | CP II, LP
Investment Holdings [Line Items]
Nonmarketable securities	7,454	7,122
Consolidated venture capital and private equity fund investments | Other venture capital and private equity fund investments
Investment Holdings [Line Items]
Nonmarketable securities	60,771	43,134
Debt funds
Investment Holdings [Line Items]
Nonmarketable securities	5,826	5,826
Debt funds | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Nonmarketable securities	3,901	3,901
Debt funds | Other debt funds
Investment Holdings [Line Items]
Nonmarketable securities	1,925	1,925
Other investments
Investment Holdings [Line Items]
Nonmarketable securities	127,264	121,721
Other investments | SPD Silicon Valley Bank Co., Ltd.
Investment Holdings [Line Items]
Nonmarketable securities	79,415	76,412
Other investments | Other investments
Investment Holdings [Line Items]
Nonmarketable securities	$ 47,849	$ 45,309
Non-marketable securities | Consolidated venture capital and private equity fund investments | Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Percentage of ownership	8.60%	8.60%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Percentage of ownership	5.90%	5.90%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Percentage of ownership	5.00%	5.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | CP II, LP
Investment Holdings [Line Items]
Percentage of ownership	5.10%	5.10%
Non-marketable securities | Consolidated venture capital and private equity fund investments | CP II, LP | Direct ownership interest
Investment Holdings [Line Items]
Percentage of ownership	1.30%
Non-marketable securities | Consolidated venture capital and private equity fund investments | CP II, LP | Indirect ownership interest
Investment Holdings [Line Items]
Percentage of ownership	3.80%
Non-marketable securities | Debt funds | Direct ownership interest
Investment Holdings [Line Items]
Percentage of ownership	11.50%
Non-marketable securities | Debt funds | Indirect ownership interest
Investment Holdings [Line Items]
Percentage of ownership	4.00%
Non-marketable securities | Debt funds | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Percentage of ownership	15.50%	15.50%
Non-marketable securities | Other investments | SPD Silicon Valley Bank Co., Ltd.
Investment Holdings [Line Items]
Percentage of ownership	50.00%	50.00%