Credit Quality - Schedule of Age Analysis of its Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	$ 88,124	$ 103,765
Loans, Total Past Due	187,248	218,531
Loans, Current & Other	10,264,414	9,180,421
Total Financing Receivables	10,451,662	9,398,952
Loans, Recorded Investment >90 Days & Accruing	11,387	11,628
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	99,124	114,766
Construction & Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	5,126	2,412
Loans, Total Past Due	13,691	17,828
Loans, Current & Other	1,250,660	1,255,226
Total Financing Receivables	1,264,351	1,273,054
Loans, Recorded Investment >90 Days & Accruing	254	1,347
Construction & Land Development [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	8,565	15,416
Commercial Real Estate [Member] \| Owner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	5,834	8,639
Loans, Total Past Due	10,314	18,470
Loans, Current & Other	854,893	909,276
Total Financing Receivables	865,207	927,746
Loans, Recorded Investment >90 Days & Accruing	650	400
Commercial Real Estate [Member] \| Owner-Occupied [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	4,480	9,831
Commercial Real Estate [Member] \| Nonowner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	12,940	24,209
Loans, Total Past Due	39,659	50,335
Loans, Current & Other	3,641,165	2,846,032
Total Financing Receivables	3,680,824	2,896,367
Loans, Recorded Investment >90 Days & Accruing	4,262	552
Commercial Real Estate [Member] \| Nonowner-Occupied [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	26,719	26,126
Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	24,881	14,888
Loans, Total Past Due	55,197	48,185
Loans, Current & Other	1,632,554	1,554,037
Total Financing Receivables	1,687,751	1,602,222
Loans, Recorded Investment >90 Days & Accruing	601	3,643
Other Commercial [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	30,316	33,297
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	29,319	44,312
Loans, Total Past Due	56,619	72,644
Loans, Current & Other	2,330,098	2,196,041
Total Financing Receivables	2,386,717	2,268,685
Loans, Recorded Investment >90 Days & Accruing	4,077	4,294
Residential Real Estate [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	27,300	28,332
Consumer [Member] \| Bankcard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	370	223
Loans, Total Past Due	496	391
Loans, Current & Other	12,084	11,262
Total Financing Receivables	12,580	11,653
Loans, Recorded Investment >90 Days & Accruing	126	168
Consumer [Member] \| Bankcard [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	126	168
Consumer [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	9,654	9,082
Loans, Total Past Due	11,272	10,678
Loans, Current & Other	542,960	408,547
Total Financing Receivables	554,232	419,225
Loans, Recorded Investment >90 Days & Accruing	1,417	1,224
Consumer [Member] \| Other Consumer [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	$ 1,618	$ 1,596

Financing receivables that are 30-89 days past due as of the balance sheet date.

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Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5111-111524

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Financing receivables that are current.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953401-111524

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Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes 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 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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