Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 149,714	$ 106,607	$ 135,859	$ 99,542
Provision for loan losses	5,045	6,810	42,734	17,845
Charge-offs	(8,516)	(7,604)	(39,194)	(18,186)
Recoveries	3,530	4,560	10,374	11,172
Net charge-offs	(4,986)	(3,044)	(28,820)	(7,014)
Ending balance	149,773	110,373	149,773	110,373
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	47,578	42,425	42,993	44,273
Provision for loan losses	4,632	2,909	14,315	3,596
Charge-offs	(4,036)	(4,074)	(10,754)	(8,580)
Recoveries	957	1,959	2,577	3,930
Net charge-offs	(3,079)	(2,115)	(8,177)	(4,650)
Ending balance	49,131	43,219	49,131	43,219
Commercial and industrial, Energy [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	66,339	26,300	54,696	14,919
Provision for loan losses	(3,231)	1,284	26,170	12,662
Charge-offs	(884)	0	(18,644)	0
Recoveries	19	0	21	3
Net charge-offs	(865)	0	(18,623)	3
Ending balance	62,243	27,584	62,243	27,584
Commercial Real Estate Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	27,063	24,935	24,313	27,163
Provision for loan losses	1,886	746	4,085	(1,470)
Charge-offs	(9)	(107)	(56)	(585)
Recoveries	277	309	875	775
Net charge-offs	268	202	819	190
Ending balance	29,217	25,883	29,217	25,883
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,935	4,702	4,659	5,178
Provision for loan losses	427	324	(470)	(205)
Charge-offs	(287)	(423)	(464)	(524)
Recoveries	92	201	442	355
Net charge-offs	(195)	(222)	(22)	(169)
Ending balance	4,167	4,804	4,167	4,804
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,799	8,245	9,198	8,009
Provision for loan losses	1,331	1,547	(1,366)	3,262
Charge-offs	(3,300)	(3,000)	(9,276)	(8,497)
Recoveries	2,185	2,091	6,459	6,109
Net charge-offs	(1,115)	(909)	(2,817)	(2,388)
Ending balance	$ 5,015	$ 8,883	$ 5,015	$ 8,883

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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- Definition

Amount of other addition (reduction) in allowance reserve for credit loss.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

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Amount of expense related to estimated loss from loan and lease transactions.

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