Loans - Summary of Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	$ 252,409	$ 358,666
Total loans	13,895,276	12,324,817
30-59 days past due	44,652	60,155
60-89 days past due	12,503	22,018
Greater than 90 days past due	44,981	53,143
Total past due	102,136	135,316
Current	13,793,140	12,189,501
Recorded investment > 90 days and accruing	4,825	10,387
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	6,195	23,390
Total loans	6,044,060	5,064,224
30-59 days past due	4,380	13,627
60-89 days past due	1,742	3,535
Greater than 90 days past due	8,560	6,270
Total past due	14,682	23,432
Current	6,029,378	5,040,792
Recorded investment > 90 days and accruing	630	1,062
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	11,674	20,229
Total loans	1,106,761	915,541
30-59 days past due	6,731	6,739
60-89 days past due	1,532	2,793
Greater than 90 days past due	5,556	8,670
Total past due	13,819	18,202
Current	1,092,942	897,339
Recorded investment > 90 days and accruing	142	541
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	27,808	53,165
Total loans	3,144,048	3,042,841
30-59 days past due	10,388	11,920
60-89 days past due	3,246	7,089
Greater than 90 days past due	15,258	24,321
Total past due	28,892	43,330
Current	3,115,156	2,999,511
Recorded investment > 90 days and accruing	957	6,273
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	187,033	209,018
Total loans	1,894,181	1,720,614
30-59 days past due	14,730	18,042
60-89 days past due	3,533	6,568
Greater than 90 days past due	11,208	9,046
Total past due	29,471	33,656
Current	1,864,710	1,686,958
Recorded investment > 90 days and accruing	1,199	72
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	19,699	52,864
Total loans	1,706,226	1,581,597
30-59 days past due	8,423	9,827
60-89 days past due	2,450	2,033
Greater than 90 days past due	4,399	4,836
Total past due	15,272	16,696
Current	1,690,954	1,564,901
Recorded investment > 90 days and accruing	1,897	2,439
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,810,199	9,494,132
30-59 days past due	40,679	46,908
60-89 days past due	11,949	13,994
Greater than 90 days past due	41,820	32,756
Total past due	94,448	93,658
Current	12,715,751	9,400,474
Recorded investment > 90 days and accruing	4,564	3,298
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial non-real estate	5,917,728	4,113,837
30-59 days past due	4,380	11,645
60-89 days past due	1,742	1,203
Greater than 90 days past due	8,560	4,803
Total past due	14,682	17,651
Current	5,903,046	4,096,186
Recorded investment > 90 days and accruing	630	521
Originated Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Construction and land development	1,073,964	752,381
30-59 days past due	6,620	5,877
60-89 days past due	1,532	1,264
Greater than 90 days past due	4,453	5,970
Total past due	12,605	13,111
Current	1,061,359	739,270
Recorded investment > 90 days and accruing	142
Originated Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial real estate	2,428,195	2,022,528
30-59 days past due	6,527	8,178
60-89 days past due	2,964	5,744
Greater than 90 days past due	13,234	14,620
Total past due	22,725	28,542
Current	2,405,470	1,993,986
Recorded investment > 90 days and accruing	696	420
Originated Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Residential mortgages	1,704,770	1,196,256
30-59 days past due	14,730	12,410
60-89 days past due	3,261	3,870
Greater than 90 days past due	11,208	3,540
Total past due	29,199	19,820
Current	1,675,571	1,176,436
Recorded investment > 90 days and accruing	1,199
Originated Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Consumer	1,685,542	1,409,130
30-59 days past due	8,422	8,798
60-89 days past due	2,450	1,913
Greater than 90 days past due	4,365	3,823
Total past due	15,237	14,534
Current	1,670,305	1,394,596
Recorded investment > 90 days and accruing	1,897	2,357
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	832,668	2,472,019
30-59 days past due	3,972	13,247
60-89 days past due	282	8,024
Greater than 90 days past due	1,591	18,170
Total past due	5,845	39,441
Current	826,823	2,432,578
Recorded investment > 90 days and accruing	261	7,089
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial non-real estate	120,137	926,997
30-59 days past due		1,982
60-89 days past due		2,332
Greater than 90 days past due		1,467
Total past due		5,781
Current	120,137	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 Construction and land development	21,123	142,931
30-59 days past due	111	862
60-89 days past due		1,529
Greater than 90 days past due		1,161
Total past due	111	3,552
Current	21,012	139,379
Recorded investment > 90 days and accruing		541
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial real estate	688,045	967,148
30-59 days past due	3,861	3,742
60-89 days past due	282	1,345
Greater than 90 days past due	1,591	9,026
Total past due	5,734	14,113
Current	682,311	953,035
Recorded investment > 90 days and accruing	261	5,853
Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Residential mortgages	2,378	315,340
30-59 days past due		5,632
60-89 days past due		2,698
Greater than 90 days past due		5,503
Total past due		13,833
Current	2,378	301,507
Recorded investment > 90 days and accruing		72
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Consumer	985	119,603
30-59 days past due		1,029
60-89 days past due		120
Greater than 90 days past due		1,013
Total past due		2,162
Current	985	117,441
Recorded investment > 90 days and accruing		82
FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	1
60-89 days past due	272
Greater than 90 days past due	1,570	2,217
Total past due	1,843	2,217
Current	250,566	356,449
FDIC Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,195	23,390
FDIC Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	1,103	1,539
Total past due	1,103	1,539
Current	10,571	18,690
FDIC Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	433	675
Total past due	433	675
Current	27,375	52,490
FDIC Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
60-89 days past due	272
Greater than 90 days past due		3
Total past due	272	3
Current	186,761	209,015
FDIC Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
30-59 days past due	1
Greater than 90 days past due	34
Total past due	35
Current	$ 19,664	$ 52,864