Investment Securities - Non-marketable and Other Securities (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Investment	Dec. 31, 2015 USD ($) Investment	Dec. 31, 2014 USD ($) Investment
Investment Holdings [Line Items]
Non-marketable securities	$ 82,823	$ 85,705
Amortization method qualified affordable housing project investments	112,447	154,356
Total non-marketable and other securities	622,552	674,946
Qualified Affordable Housing Project Investments, Commitment	58,095	90,978
Tax Credits And Other Tax Benefits Recognized	15,404	14,375	$ 12,109
Amortization Expense Included In Provision For Income Taxes	$ 12,145	$ 10,389	$ 9,340
Upper Limit
Investment Holdings [Line Items]
Ownership interest percentage	5.00%	5.00%
Fair value accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 753	$ 548
Venture capital and private equity fund investments | Fair value accounting
Investment Holdings [Line Items]
Non-marketable securities	141,649	152,237
Non-marketable securities	222,000	233,000
Venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 18,459	$ 20,794
Ownership percentage of each Fund	12.60%	12.60%
Venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund II, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 7,720	$ 10,035
Ownership percentage of each Fund	8.60%	8.60%
Venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund III, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 20,449	$ 23,926
Ownership percentage of each Fund	5.90%	5.90%
Venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund IV, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 24,530	$ 26,411
Ownership percentage of each Fund	5.00%	5.00%
Venture capital and private equity fund investments | Fair value accounting | Strategic Investors Fund V Funds
Investment Holdings [Line Items]
Non-marketable securities	$ 12,029	$ 10,470
Venture capital and private equity fund investments | Fair value accounting | Capital Preferred Return Fund, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 57,627	$ 60,619
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	$ 59,718	$ 62,983
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	$ 5,845	$ 7,841
Ownership percentage of each Fund	58.20%	58.20%
Venture capital and private equity fund investments | Fair value accounting | Other private equity fund | Direct ownership interest
Investment Holdings [Line Items]
Ownership percentage of each Fund	41.50%
Venture capital and private equity fund investments | Fair value accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	$ 18,095	$ 14,863
Venture capital and private equity fund investments | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities	82,823	85,705
Venture capital and private equity fund investments | Cost method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 114,606	$ 120,676
Number of investments | Investment	252	267	281
Other venture capital investments | Fair value accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 2,040	$ 2,040
Other venture capital investments | Fair value accounting | CP I, L.P.
Investment Holdings [Line Items]
Non-marketable securities	$ 2,040	$ 2,040
Ownership percentage of each Fund	10.70%	10.70%
Debt Securities | Equity method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 17,020	$ 21,970
Debt Securities | Equity method accounting | Gold Hill Capital 2008, LP
Investment Holdings [Line Items]
Non-marketable securities	$ 13,557	$ 17,453
Ownership percentage of each Fund	15.50%	15.50%
Debt Securities | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	$ 3,463	$ 4,517
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	$ 123,514	118,532
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	$ 75,296	$ 78,799
Ownership percentage of each Fund	50.00%	50.00%
Other investments | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities	$ 48,218	$ 39,733
Other investments | Cost method accounting
Investment Holdings [Line Items]
Non-marketable securities	$ 27,700	$ 18,882