Investment Securities - Non-marketable and Other Securities Additional Information (Detail) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) Investment	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Investment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) Investment
Investment Holdings [Line Items]
Investments in qualified affordable housing projects, net	$ 251,479		$ 251,479		$ 174,214
Tax credits and other tax benefits recognized	5,207	$ 3,968	10,629	$ 8,660
Amortization expense included in provision for income taxes	4,705	$ 3,385	9,497	$ 6,621
Other liabilities	$ 161,113		$ 161,113		$ 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	226		226		235
Unconsolidated venture capital and private equity fund investments	$ 211,113		$ 211,113		$ 98,548

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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Amount of investment in qualified affordable housing projects.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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Amount of commitment or contingent commitments to qualified affordable housing project investments.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64813897&loc=SL49122993-202985

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