Investment Securities - Components of Non-marketable and Other Equity Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Investments in qualified affordable housing projects, net	$ 261,706	$ 174,214
Non-marketable and other equity securities	896,249	651,053
Non-marketable securities | Equity method accounting | Consolidated venture capital and private equity fund investments
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	112,537	89,809
Non-marketable securities | Equity method accounting | Other investments
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	125,632	111,198
Non-marketable securities | Equity method accounting | Debt funds
Investment Holdings [Line Items]
Non-marketable securities, equity method accounting	5,241	21,183
Non-marketable securities | Fair value accounting | Consolidated venture capital and private equity fund investments
Investment Holdings [Line Items]
Consolidated venture capital and private equity fund investments	126,467	128,111
Non-marketable securities | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Investment Holdings [Line Items]
Unconsolidated venture capital and private equity fund investments	208,953	98,548
Non-marketable securities | Fair value accounting | Other investments
Investment Holdings [Line Items]
Other investments without a readily determinable fair value	25,253	27,680
Other equity securities | Fair value accounting
Investment Holdings [Line Items]
Other equity securities in public companies (fair value accounting)	$ 30,460	$ 310