Investment Securities - Non-marketable and Other Securities Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Investment	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Investment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) Investment
Investment Holdings [Line Items]
Investments in qualified affordable housing projects, net	$ 261,706		$ 261,706		$ 174,214
Tax credits and other tax benefits recognized	6,283	$ 4,539	16,912	$ 13,199
Amortization expense included in provision for income taxes	4,773	$ 3,533	14,269	$ 10,154
Other liabilities	$ 166,867		$ 166,867		$ 100,891
Upper Limit
Investment Holdings [Line Items]
Equity method investment voting ownership percentage	5.00%		5.00%
Non-marketable securities | Fair value accounting | Unconsolidated venture capital and private equity fund investments
Investment Holdings [Line Items]
Number of investments | Investment	220		220		235
Unconsolidated venture capital and private equity fund investments	$ 208,953		$ 208,953		$ 98,548