Deposits (Schedule of Deposits) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposit [Line Items]
Non-interest-bearing demand deposits:	$ 11,197,093	$ 10,513,369
Time Deposits, $100,000 or More	467,969
Total Interest-bearing deposits	15,675,296	15,298,206
Total deposits	26,872,389	25,811,575
Commercial And Individual [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	10,412,882	9,670,989
Correspondent Banks [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	222,648	280,751
Private Accounts [Member]
Deposit [Line Items]
Savings and interest checking	6,788,766	6,436,065
Money market accounts	7,624,471	7,486,431
Time Deposits, $100,000 or More	453,668	460,028
Time accounts under $100,000	324,636	338,714
Total private accounts	15,191,541	14,721,238
Public Funds [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	561,563	561,629
Savings and interest checking	410,140	446,872
Money market accounts	59,008	113,669
Time Deposits, $100,000 or More	14,301	15,748
Time accounts under $100,000	306	679
Total public funds	$ 483,755	$ 576,968

Deposit [Line Items]

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- Definition

Interest Bearing Deposits Public Funds

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- Definition

Interest Bearing Private Accounts Deposits

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- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

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Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).

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The aggregate of all domestic and foreign interest-bearing deposit liabilities.

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The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.

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Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E

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Amount of time deposit liabilities, including certificates of deposit, in denominations of less than $100,000.

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-Name Industry Guide
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