Loans and Allowance for Loan Losses - Schedule of Credit Quality Indicators of Various Classes of Loans - Credit Risk Profile by Internally Assigned Grade (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 1,578,583	$ 1,654,170
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,571,594	1,645,199
Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	6,989	8,971
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	4,625,315	4,433,288
Commercial Non-Real Estate [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,633,490	2,713,385
Commercial Non-Real Estate [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	967,485	1,690,643
Commercial Non-Real Estate [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	24,340	29,260
Commercial Non-Real Estate [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	4,351,662	4,214,260
Commercial Non-Real Estate [Member] | Pass [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,459,635	2,610,970
Commercial Non-Real Estate [Member] | Pass [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	877,964	1,588,435
Commercial Non-Real Estate [Member] | Pass [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	14,063	14,855
Commercial Non-Real Estate [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	148,516	84,828
Commercial Non-Real Estate [Member] | Pass-Watch [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	106,657	32,393
Commercial Non-Real Estate [Member] | Pass-Watch [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	41,741	52,361
Commercial Non-Real Estate [Member] | Pass-Watch [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	118	74
Commercial Non-Real Estate [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	59,908	33,043
Commercial Non-Real Estate [Member] | Special Mention [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	31,600	23,550
Commercial Non-Real Estate [Member] | Special Mention [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	28,308	6,267
Commercial Non-Real Estate [Member] | Special Mention [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade		3,226
Commercial Non-Real Estate [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	61,965	98,124
Commercial Non-Real Estate [Member] | Substandard [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	35,598	46,472
Commercial Non-Real Estate [Member] | Substandard [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	18,547	43,219
Commercial Non-Real Estate [Member] | Substandard [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	7,820	8,433
Commercial Non-Real Estate [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,264	3,033
Commercial Non-Real Estate [Member] | Doubtful [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Non-Real Estate [Member] | Doubtful [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	925	361
Commercial Non-Real Estate [Member] | Doubtful [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,339	2,672
Commercial Non-Real Estate [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Non-Real Estate [Member] | Loss [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Non-Real Estate [Member] | Loss [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Non-Real Estate [Member] | Loss [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	920,408	989,306
Construction and Land Development [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	738,983	665,673
Construction and Land Development [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	158,228	295,151
Construction and Land Development [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	23,197	28,482
Construction and Land Development [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	812,686	807,111
Construction and Land Development [Member] | Pass [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	681,999	557,511
Construction and Land Development [Member] | Pass [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	130,457	249,269
Construction and Land Development [Member] | Pass [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	230	331
Construction and Land Development [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	26,010	17,726
Construction and Land Development [Member] | Pass-Watch [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	16,728	13,705
Construction and Land Development [Member] | Pass-Watch [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	8,684	2,993
Construction and Land Development [Member] | Pass-Watch [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	598	1,028
Construction and Land Development [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,587	43,190
Construction and Land Development [Member] | Special Mention [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	944	30,522
Construction and Land Development [Member] | Special Mention [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,446	12,248
Construction and Land Development [Member] | Special Mention [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	197	420
Construction and Land Development [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	67,190	101,873
Construction and Land Development [Member] | Substandard [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	39,312	63,925
Construction and Land Development [Member] | Substandard [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	17,637	30,637
Construction and Land Development [Member] | Substandard [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	10,241	7,311
Construction and Land Development [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	11,935	19,406
Construction and Land Development [Member] | Doubtful [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade		10
Construction and Land Development [Member] | Doubtful [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	4	4
Construction and Land Development [Member] | Doubtful [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	11,931	19,392
Construction and Land Development [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Construction and Land Development [Member] | Loss [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Construction and Land Development [Member] | Loss [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Construction and Land Development [Member] | Loss [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,914,969	2,923,094
Commercial Real Estate [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,816,402	1,548,402
Commercial Real Estate [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,038,287	1,279,546
Commercial Real Estate [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	60,280	95,146
Commercial Real Estate [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,605,727	2,543,763
Commercial Real Estate [Member] | Pass [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,656,114	1,353,453
Commercial Real Estate [Member] | Pass [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	943,760	1,173,617
Commercial Real Estate [Member] | Pass [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,853	16,693
Commercial Real Estate [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	78,757	67,573
Commercial Real Estate [Member] | Pass-Watch [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	32,762	36,507
Commercial Real Estate [Member] | Pass-Watch [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	41,172	16,051
Commercial Real Estate [Member] | Pass-Watch [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	4,823	15,015
Commercial Real Estate [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	14,609	54,815
Commercial Real Estate [Member] | Special Mention [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,618	29,912
Commercial Real Estate [Member] | Special Mention [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	7,864	21,116
Commercial Real Estate [Member] | Special Mention [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,127	3,787
Commercial Real Estate [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	202,370	228,148
Commercial Real Estate [Member] | Substandard [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	123,890	128,088
Commercial Real Estate [Member] | Substandard [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	45,491	68,762
Commercial Real Estate [Member] | Substandard [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	32,989	31,298
Commercial Real Estate [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	13,506	28,795
Commercial Real Estate [Member] | Doubtful [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	18	442
Commercial Real Estate [Member] | Doubtful [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate [Member] | Doubtful [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	13,488	28,353
Commercial Real Estate [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate [Member] | Loss [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate [Member] | Loss [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate [Member] | Loss [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,695,197	1,577,944
Residential Mortgage Loans [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,124,649	827,985
Residential Mortgage Loans [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	223,494	263,515
Residential Mortgage Loans [Member] | Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	347,054	486,444
Residential Mortgage Loans [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,671,443	1,559,689
Residential Mortgage Loans [Member] | Performing [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,110,952	820,281
Residential Mortgage Loans [Member] | Performing [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	223,101	263,515
Residential Mortgage Loans [Member] | Performing [Member] | Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	337,390	475,893
Residential Mortgage Loans [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	23,754	18,255
Residential Mortgage Loans [Member] | Nonperforming [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	13,697	7,704
Residential Mortgage Loans [Member] | Nonperforming [Member] | Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	393
Residential Mortgage Loans [Member] | Nonperforming [Member] | Acquired [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 9,664	$ 10,551