Loans and Allowance for Loan Losses - Summary of Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	$ 392,002	$ 515,823
Total loans	11,734,472	11,577,802
30-59 days past due	33,010	85,960
60-89 days past due	15,103	28,347
Greater than 90 days past due	71,192	85,726
Total past due	119,305	200,033
Current	11,615,167	11,377,769
Recorded investment > 90 days and accruing	15,620	13,243
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	24,340	29,260
Total loans	4,625,315	4,433,288
30-59 days past due	8,955
60-89 days past due	3,305
Greater than 90 days past due	11,011
Total past due	23,271
Current	4,602,044
Recorded investment > 90 days and accruing	1,968
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	23,197	28,482
Total loans	920,408	989,306
30-59 days past due	3,564
60-89 days past due	3,028
Greater than 90 days past due	21,297
Total past due	27,889
Current	892,519
Recorded investment > 90 days and accruing	8,239
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	60,280	95,146
Total loans	2,914,969	2,923,094
30-59 days past due	14,301
60-89 days past due	2,918
Greater than 90 days past due	22,821
Total past due	40,040
Current	2,874,929
Recorded investment > 90 days and accruing	3,615
Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	223,494	263,515
Total loans	1,695,197	1,577,944
30-59 days past due	818	21,141
60-89 days past due	3,454	4,593
Greater than 90 days past due	11,022	13,489
Total past due	15,294	39,223
Current	1,679,903	1,538,721
Recorded investment > 90 days and accruing		1,106
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	60,691	99,420
Total loans	1,578,583	1,654,170
30-59 days past due	5,372	11,630
60-89 days past due	2,398	2,580
Greater than 90 days past due	5,041	6,401
Total past due	12,811	20,611
Current	1,565,772	1,633,559
Recorded investment > 90 days and accruing	1,798	2,521
Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		8,345,688
30-59 days past due		53,189
60-89 days past due		21,174
Greater than 90 days past due		65,836
Total past due		140,199
Current		8,205,489
Recorded investment > 90 days and accruing		9,616
Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered	8,700,767	7,107,221
30-59 days past due	26,403	46,246
60-89 days past due	11,959	21,961
Greater than 90 days past due	51,781	54,686
Total past due	90,143	122,893
Current	8,610,624	6,984,328
Recorded investment > 90 days and accruing	12,512	7,736
Originated loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial non-real estate	3,633,490	2,713,385
30-59 days past due	7,369
60-89 days past due	2,891
Greater than 90 days past due	9,615
Total past due	19,875
Current	3,613,615
Recorded investment > 90 days and accruing	1,268
Originated loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Construction and land development	738,983	665,673
30-59 days past due	2,083
60-89 days past due	2,131
Greater than 90 days past due	18,079
Total past due	22,293
Current	716,690
Recorded investment > 90 days and accruing	8,183
Originated loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial real estate	1,816,402	1,548,402
30-59 days past due	11,753
60-89 days past due	2,215
Greater than 90 days past due	16,383
Total past due	30,351
Current	1,786,051
Recorded investment > 90 days and accruing	1,309
Originated loans [Member] | Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Residential mortgages	1,124,649	827,985
30-59 days past due	224	11,500
60-89 days past due	2,484	3,303
Greater than 90 days past due	4,018	4,100
Total past due	6,726	18,903
Current	1,117,923	809,082
Recorded investment > 90 days and accruing
Originated loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Consumer	1,387,243	1,351,776
30-59 days past due	4,974	10,348
60-89 days past due	2,238	2,150
Greater than 90 days past due	3,686	4,231
Total past due	10,898	16,729
Current	1,376,345	1,335,047
Recorded investment > 90 days and accruing	1,752	2,474
Originated loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial non-real estate		4,927,460
30-59 days past due		24,398
60-89 days past due		16,508
Greater than 90 days past due		46,355
Total past due		87,261
Current		4,840,199
Recorded investment > 90 days and accruing		5,262
Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered	2,641,703	3,954,758
30-59 days past due	6,602	39,714
60-89 days past due	3,142	6,386
Greater than 90 days past due	15,123	26,940
Total past due	24,867	73,040
Current	2,616,836	3,881,718
Recorded investment > 90 days and accruing	3,108	5,507
Acquired loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial non-real estate	967,485	1,690,643
30-59 days past due	1,586
60-89 days past due	414
Greater than 90 days past due	1,396
Total past due	3,396
Current	964,089
Recorded investment > 90 days and accruing	700
Acquired loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Construction and land development	158,228	295,151
30-59 days past due	1,481
60-89 days past due	897
Greater than 90 days past due	594
Total past due	2,972
Current	155,256
Recorded investment > 90 days and accruing	56
Acquired loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial real estate	1,038,287	1,279,546
30-59 days past due	2,548
60-89 days past due	703
Greater than 90 days past due	5,763
Total past due	9,014
Current	1,029,273
Recorded investment > 90 days and accruing	2,306
Acquired loans [Member] | Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Residential mortgages	347,054	486,444
30-59 days past due	594	9,641
60-89 days past due	970	1,290
Greater than 90 days past due	6,337	8,996
Total past due	7,901	19,927
Current	339,153	466,517
Recorded investment > 90 days and accruing		1,106
Acquired loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Consumer	130,649	202,974
30-59 days past due	393	1,282
60-89 days past due	158	430
Greater than 90 days past due	1,033	2,170
Total past due	1,584	3,882
Current	129,065	199,092
Recorded investment > 90 days and accruing	46	47
Acquired loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial non-real estate		3,265,340
30-59 days past due		28,791
60-89 days past due		4,666
Greater than 90 days past due		15,774
Total past due		49,231
Current		3,216,109
Recorded investment > 90 days and accruing		4,354
Covered loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	392,002	515,823
30-59 days past due	5
60-89 days past due	2
Greater than 90 days past due	4,288	4,100
Total past due	4,295	4,100
Current	387,707	511,723
Recorded investment > 90 days and accruing
Covered loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	24,340
30-59 days past due
60-89 days past due
Greater than 90 days past due
Total past due
Current	24,340
Recorded investment > 90 days and accruing
Covered loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	23,197
30-59 days past due
60-89 days past due
Greater than 90 days past due	2,624
Total past due	2,624
Current	20,573
Recorded investment > 90 days and accruing
Covered loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	60,280
30-59 days past due
60-89 days past due
Greater than 90 days past due	675
Total past due	675
Current	59,605
Recorded investment > 90 days and accruing
Covered loans [Member] | Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	223,494	263,515
30-59 days past due
60-89 days past due
Greater than 90 days past due	667	393
Total past due	667	393
Current	222,827	263,122
Recorded investment > 90 days and accruing
Covered loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	60,691	99,420
30-59 days past due	5
60-89 days past due	2
Greater than 90 days past due	322
Total past due	329
Current	60,362	99,420
Recorded investment > 90 days and accruing
Covered loans [Member] | Commercial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans		152,888
60-89 days past due
Greater than 90 days past due		3,707
Total past due		3,707
Current		149,181
Recorded investment > 90 days and accruing