Loans and Allowance for Loan Losses - Summary of Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	$ 280,830	$ 358,666
Total loans	13,348,574	12,324,817
30-59 days past due	15,255	60,155
60-89 days past due	17,262	22,018
Greater than 90 days past due	43,884	53,143
Total past due	76,401	135,316
Current	13,272,173	12,189,501
Recorded investment > 90 days and accruing	6,667	10,374
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	11,171	23,390
Total loans	5,587,137	5,064,224
30-59 days past due	4,288	13,627
60-89 days past due	4,134	3,535
Greater than 90 days past due	4,845	6,270
Total past due	13,267	23,432
Current	5,573,870	5,040,792
Recorded investment > 90 days and accruing	259	1,062
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	11,166	20,229
Total loans	1,095,902	915,541
30-59 days past due	1,390	6,739
60-89 days past due	2,300	2,793
Greater than 90 days past due	7,585	8,670
Total past due	11,275	18,202
Current	1,084,627	897,339
Recorded investment > 90 days and accruing	1,460	541
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	41,550	53,165
Total loans	3,100,834	3,042,841
30-59 days past due	4,046	11,920
60-89 days past due	2,811	7,089
Greater than 90 days past due	15,805	24,321
Total past due	22,662	43,330
Current	3,078,172	2,999,511
Recorded investment > 90 days and accruing	1,728	6,273
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	185,289	209,018
Total loans	1,858,490	1,720,614
30-59 days past due	633	18,042
60-89 days past due	5,220	6,568
Greater than 90 days past due	10,731	9,046
Total past due	16,584	33,656
Current	1,841,906	1,686,958
Recorded investment > 90 days and accruing	220	72
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total covered loans	31,654	52,864
Total loans	1,706,211	1,581,597
30-59 days past due	4,898	9,827
60-89 days past due	2,797	2,033
Greater than 90 days past due	4,918	4,836
Total past due	12,613	16,696
Current	1,693,598	1,564,901
Recorded investment > 90 days and accruing	3,000	2,426
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered	11,285,568	9,494,132
30-59 days past due	13,965	46,908
60-89 days past due	14,487	13,994
Greater than 90 days past due	36,360	32,756
Total past due	64,812	93,658
Current	11,220,756	9,400,474
Recorded investment > 90 days and accruing	5,149	3,285
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial non-real estate	4,806,740	4,113,837
30-59 days past due	4,137	11,645
60-89 days past due	4,039	1,203
Greater than 90 days past due	3,111	4,803
Total past due	11,287	17,651
Current	4,795,453	4,096,186
Recorded investment > 90 days and accruing	259	521
Originated Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Construction and land development	974,442	752,381
30-59 days past due	1,159	5,877
60-89 days past due	651	1,264
Greater than 90 days past due	6,185	5,970
Total past due	7,995	13,111
Current	966,447	739,270
Recorded investment > 90 days and accruing	1,443
Originated Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial real estate	2,245,855	2,022,528
30-59 days past due	3,524	8,178
60-89 days past due	2,170	5,744
Greater than 90 days past due	12,271	14,620
Total past due	17,965	28,542
Current	2,227,890	1,993,986
Recorded investment > 90 days and accruing	257	420
Originated Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Residential mortgages	1,635,462	1,196,256
30-59 days past due	606	12,410
60-89 days past due	5,071	3,870
Greater than 90 days past due	10,503	3,540
Total past due	16,180	19,820
Current	1,619,282	1,176,436
Recorded investment > 90 days and accruing	220
Originated Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Consumer	1,623,069	1,409,130
30-59 days past due	4,539	8,798
60-89 days past due	2,556	1,913
Greater than 90 days past due	4,290	3,823
Total past due	11,385	14,534
Current	1,611,684	1,394,596
Recorded investment > 90 days and accruing	2,970	2,344
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered	1,782,176	2,472,019
30-59 days past due	1,289	13,247
60-89 days past due	2,626	8,024
Greater than 90 days past due	7,489	18,170
Total past due	11,404	39,441
Current	1,770,772	2,432,578
Recorded investment > 90 days and accruing	1,518	7,089
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial non-real estate	769,226	926,997
30-59 days past due	151	1,982
60-89 days past due	95	2,332
Greater than 90 days past due	1,734	1,467
Total past due	1,980	5,781
Current	767,246	921,216
Recorded investment > 90 days and accruing		541
Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Construction and land development	110,294	142,931
30-59 days past due	231	862
60-89 days past due	1,649	1,529
Greater than 90 days past due	1,400	1,161
Total past due	3,280	3,552
Current	107,014	139,379
Recorded investment > 90 days and accruing	17	541
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Commercial real estate	813,429	967,148
30-59 days past due	522	3,742
60-89 days past due	641	1,345
Greater than 90 days past due	3,534	9,026
Total past due	4,697	14,113
Current	808,732	953,035
Recorded investment > 90 days and accruing	1,471	5,853
Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Residential mortgages	37,739	315,340
30-59 days past due	27	5,632
60-89 days past due		2,698
Greater than 90 days past due	228	5,503
Total past due	255	13,833
Current	37,484	301,507
Recorded investment > 90 days and accruing		72
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total-excluding covered-Consumer	51,488	119,603
30-59 days past due	358	1,029
60-89 days past due	241	120
Greater than 90 days past due	593	1,013
Total past due	1,192	2,162
Current	50,296	117,441
Recorded investment > 90 days and accruing	30	82
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	1
60-89 days past due	149
Greater than 90 days past due	35	2,217
Total past due	185	2,217
Current	280,645	356,449
Recorded investment > 90 days and accruing
Covered Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due
60-89 days past due
Greater than 90 days past due
Total past due
Current	11,171	23,390
Recorded investment > 90 days and accruing
Covered Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due
60-89 days past due
Greater than 90 days past due		1,539
Total past due		1,539
Current	11,166	18,690
Recorded investment > 90 days and accruing
Covered Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due
60-89 days past due
Greater than 90 days past due		675
Total past due		675
Current	41,550	52,490
Covered Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due
60-89 days past due	149
Greater than 90 days past due		3
Total past due	149	3
Current	185,140	209,015
Recorded investment > 90 days and accruing
Covered Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	1
60-89 days past due
Greater than 90 days past due	35
Total past due	36
Current	31,618	52,864
Recorded investment > 90 days and accruing