Investment Securities - Non-marketable and Other Securities (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Investment	Dec. 31, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment
Investment Holdings [Line Items]
Non-marketable securities	$ 89,809	$ 82,823
Amortization method qualified affordable housing project investments	174,214	112,447
Total non-marketable and other securities	651,053	622,552
Qualified Affordable Housing Project Investments, Commitment	100,891	58,095
Tax Credits And Other Tax Benefits Recognized	17,296	15,404	$ 14,375
Amortization Expense Included In Provision For Income Taxes	17,362	$ 12,145	$ 10,389
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 33,800
Upper Limit
Investment Holdings [Line Items]
Ownership interest percentage	5.00%	5.00%
Venture capital and private equity fund investments | Fair value accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 127,192	$ 141,649
Non-marketable securities	202,000	222,000
Venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 14,673	$ 18,459
Ownership percentage of each Fund	12.60%	12.60%
Venture capital and private equity fund investments | Fair value accounting | CP II, L.P. | Direct ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund	1.30%
Venture capital and private equity fund investments | Fair value accounting | CP II, L.P. | Indirect ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund	3.80%
Venture capital and private equity fund investments | Fair value accounting | Capital Preferred Return Fund, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 54,147	$ 57,627
Ownership percentage of each Fund	20.00%	20.00%
Venture capital and private equity fund investments | Fair value accounting | Growth Partners, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 58,372	$ 59,718
Ownership percentage of each Fund	33.00%	33.00%
Venture capital and private equity fund investments | Fair value accounting | Other private equity fund
Investment Holdings [Line Items]
Non-marketable securities	$ 0	$ 5,845
Ownership percentage of each Fund	0.00%	58.20%
Venture capital and private equity fund investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 89,809	$ 82,823
Venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund II, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 6,342	$ 7,720
Ownership percentage of each Fund	8.60%	8.60%
Venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund III, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 18,758	$ 20,449
Ownership percentage of each Fund	5.90%	5.90%
Venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund IV, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 25,551	$ 24,530
Ownership percentage of each Fund	5.00%	5.00%
Venture capital and private equity fund investments | Equity method accounting | Strategic Investors Fund V Funds
Investment Holdings [Line Items]
Non-marketable securities	$ 16,856	$ 12,029
Venture capital and private equity fund investments | Equity method accounting | CP II, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 6,700	$ 7,798
Ownership percentage of each Fund	5.10%	5.10%
Venture capital and private equity fund investments | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	$ 15,602	$ 10,297
Venture capital and private equity fund investments | Cost method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 99,000	$ 115,000
Number of investments | Investment	235	252	267
Other venture capital investments | Fair value accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 919	$ 2,040
Other venture capital investments | Fair value accounting | CP I, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 919	$ 2,040
Ownership percentage of each Fund	10.70%	10.70%
Debt Securities | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 21,183	$ 17,020
Debt Securities | Equity method accounting | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Non-marketable securities	$ 18,690	$ 13,557
Ownership percentage of each Fund	15.50%	15.50%
Debt Securities | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	$ 2,493	$ 3,463
Other investments | Fair value accounting | Capital Preferred Return Fund, L.P. | Indirect ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund		4.10%
Other investments | Fair value accounting | Growth Partners, L.P. | Indirect ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund		12.60%
Other investments | Fair value accounting | Other private equity fund | Direct ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund		41.50%
Other investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 111,198	$ 123,514
Other investments | Equity method accounting | Gold Hill Capital 2008, LP | Direct ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund	11.50%
Other investments | Equity method accounting | Gold Hill Capital 2008, LP | Indirect ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund	4.00%
Other investments | Equity method accounting | China Joint Venture investment
Investment Holdings [Line Items]
Non-marketable securities	$ 75,337	$ 75,296
Ownership percentage of each Fund	50.00%	50.00%
Other investments | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	$ 35,861	$ 48,218
Other investments | Cost method accounting
Investment Holdings [Line Items]
Non-marketable securities	27,680	27,700
Low Income Housing Tax Credit Funds
Investment Holdings [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	3,800
Other securities | Fair value accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 310	$ 753