Investment Securities - Nonmarketable Securities Under Equity Method Accounting (Details) - Equity method accounting - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Consolidated venture capital and private equity fund investments
Investment Holdings [Line Items]
Nonmarketable securities	$ 129,485	$ 89,809
Consolidated venture capital and private equity fund investments | Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Nonmarketable securities	4,670	6,342
Consolidated venture capital and private equity fund investments | Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Nonmarketable securities	17,396	18,758
Consolidated venture capital and private equity fund investments | Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Nonmarketable securities	28,974	25,551
Consolidated venture capital and private equity fund investments | Strategic Investors Fund V funds
Investment Holdings [Line Items]
Nonmarketable securities	28,189	16,856
Consolidated venture capital and private equity fund investments | CP II, LP
Investment Holdings [Line Items]
Nonmarketable securities	7,122	6,700
Consolidated venture capital and private equity fund investments | Other venture capital and private equity fund investments
Investment Holdings [Line Items]
Nonmarketable securities	43,134	15,602
Debt funds
Investment Holdings [Line Items]
Nonmarketable securities	5,826	21,183
Debt funds | Gold Hill Capital 2008, LP (ii)
Investment Holdings [Line Items]
Nonmarketable securities	3,901	18,690
Debt funds | Other debt funds
Investment Holdings [Line Items]
Nonmarketable securities	1,925	2,493
Other investments
Investment Holdings [Line Items]
Nonmarketable securities	121,721	111,198
Other investments | SPD Silicon Valley Bank Co., Ltd.
Investment Holdings [Line Items]
Nonmarketable securities	76,412	75,337
Other investments | Other investments
Investment Holdings [Line Items]
Nonmarketable securities	$ 45,309	$ 35,861
Non-marketable securities | Consolidated venture capital and private equity fund investments | Strategic Investors Fund II, LP
Investment Holdings [Line Items]
Ownership interest percentage	8.60%	8.60%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Strategic Investors Fund III, LP
Investment Holdings [Line Items]
Ownership interest percentage	5.90%	5.90%
Non-marketable securities | Consolidated venture capital and private equity fund investments | Strategic Investors Fund IV, LP
Investment Holdings [Line Items]
Ownership interest percentage	5.00%	5.00%
Non-marketable securities | Consolidated venture capital and private equity fund investments | CP II, LP
Investment Holdings [Line Items]
Ownership interest percentage	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]
Ownership interest percentage	1.30%
Non-marketable securities | Consolidated venture capital and private equity fund investments | CP II, LP | Indirect ownership interest
Investment Holdings [Line Items]
Ownership interest percentage	3.80%
Non-marketable securities | Debt funds | Direct ownership interest
Investment Holdings [Line Items]
Ownership interest percentage	11.50%
Non-marketable securities | Debt funds | Indirect ownership interest
Investment Holdings [Line Items]
Ownership interest percentage	4.00%
Non-marketable securities | Debt funds | Gold Hill Capital 2008, LP (ii)
Investment Holdings [Line Items]
Ownership interest percentage	15.50%	15.50%
Non-marketable securities | Other investments | SPD Silicon Valley Bank Co., Ltd.
Investment Holdings [Line Items]
Ownership interest percentage	50.00%	50.00%