Loans - Narrative (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Loans, net of unearned income	$ 19,795,085		$ 19,795,085		$ 15,064,971
Deferred loan origination fees	26,200		26,200		22,600
Deposit liabilities reclassified as loans receivable	4,800		4,800		4,200
Loans with carrying value pledged to secure public deposits and other borrowings	5,000,000		5,000,000		4,500,000
Troubled debt restructurings	24,586	$ 75,068	51,517	$ 218,596
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Loans, net of unearned income	3,024,970		3,024,970		$ 1,267,400
Sabadell United \| Covered Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Loans, net of unearned income	169,200		169,200
Troubled Debt Restructurings
Accounts, Notes, Loans and Financing Receivable
Troubled debt restructurings	24,586	75,068	51,500	218,600
Troubled debt restructurings on accrual status	22,900	25,400	40,500	94,300
Troubled debt restructurings on nonaccrual status	$ 1,700	$ 49,700	$ 11,000	$ 124,300

Financing Receivable, Modifications, Post-Modification Recorded Investment, Nonaccrual Status

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- Definition

Financing Receivable, Modifications, Post-Modification Recorded Investment, Past Due

+ References

No definition available.

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans, including loans covered under loss sharing agreements.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=50488274&loc=d3e64164-112818

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- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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