Loans - Summary of Age Analysis of Past Due Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	$ 203,297	$ 252,409
Total loans	15,703,314	13,895,276
Total past due	153,691	102,136
Current	15,549,623	13,793,140
Recorded investment > 90 days and accruing	7,653	4,825
30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	79,027	44,652
60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	12,101	12,503
Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	62,563	44,981
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	5,528	6,195
Total loans	6,995,824	6,044,060
Total past due	43,881	14,682
Current	6,951,943	6,029,378
Recorded investment > 90 days and accruing	3,060	630
Commercial Non-Real Estate [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	17,406	4,380
Commercial Non-Real Estate [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,468	1,742
Commercial Non-Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	25,007	8,560
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	7,127	11,674
Total loans	1,151,950	1,106,761
Total past due	24,365	13,819
Current	1,127,585	1,092,942
Recorded investment > 90 days and accruing	1,230	142
Construction and Land Development [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	19,886	6,731
Construction and Land Development [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	436	1,532
Construction and Land Development [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	4,043	5,556
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	15,582	27,808
Total loans	3,412,551	3,144,048
Total past due	21,202	28,892
Current	3,391,349	3,115,156
Recorded investment > 90 days and accruing	1,034	957
Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	6,769	10,388
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,405	3,246
Commercial Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	13,028	15,258
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	162,241	187,033
Total loans	2,049,524	1,894,181
Total past due	34,857	29,471
Current	2,014,667	1,864,710
Recorded investment > 90 days and accruing	163	1,199
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	18,657	14,730
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	4,360	3,533
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	11,840	11,208
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	12,819	19,699
Total loans	2,093,465	1,706,226
Total past due	29,386	15,272
Current	2,064,079	1,690,954
Recorded investment > 90 days and accruing	2,166	1,897
Consumer [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	16,309	8,423
Consumer [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	4,432	2,450
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	8,645	4,399
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	15,258,587	12,810,199
Total past due	153,075	94,448
Current	15,105,512	12,715,751
Recorded investment > 90 days and accruing	7,653	4,564
Originated Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	79,012	40,679
Originated Loans [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	12,025	11,949
Originated Loans [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	62,038	41,820
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial non-real estate	6,930,453	5,917,728
Total past due	43,881	14,682
Current	6,886,572	5,903,046
Recorded investment > 90 days and accruing	3,060	630
Originated Loans [Member] | Commercial Non-Real Estate [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	17,406	4,380
Originated Loans [Member] | Commercial Non-Real Estate [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,468	1,742
Originated Loans [Member] | Commercial Non-Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	25,007	8,560
Originated Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Construction and land development	1,139,743	1,073,964
Total past due	24,365	12,605
Current	1,115,378	1,061,359
Recorded investment > 90 days and accruing	1,230	142
Originated Loans [Member] | Construction and Land Development [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	19,886	6,620
Originated Loans [Member] | Construction and Land Development [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	436	1,532
Originated Loans [Member] | Construction and Land Development [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	4,043	4,453
Originated Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial real estate	3,220,509	2,428,195
Total past due	20,586	22,725
Current	3,199,923	2,405,470
Recorded investment > 90 days and accruing	1,034	696
Originated Loans [Member] | Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	6,754	6,527
Originated Loans [Member] | Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	1,329	2,964
Originated Loans [Member] | Commercial Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	12,503	13,234
Originated Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Residential mortgages	1,887,256	1,704,770
Total past due	34,857	29,199
Current	1,852,399	1,675,571
Recorded investment > 90 days and accruing	163	1,199
Originated Loans [Member] | Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	18,657	14,730
Originated Loans [Member] | Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	4,360	3,261
Originated Loans [Member] | Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	11,840	11,208
Originated Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Consumer	2,080,626	1,685,542
Total past due	29,386	15,237
Current	2,051,240	1,670,305
Recorded investment > 90 days and accruing	2,166	1,897
Originated Loans [Member] | Consumer [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	16,309	8,422
Originated Loans [Member] | Consumer [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	4,432	2,450
Originated Loans [Member] | Consumer [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	8,645	4,365
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	241,430	832,668
Total past due	616	5,845
Current	240,814	826,823
Recorded investment > 90 days and accruing		261
Acquired Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	15	3,972
Acquired Loans [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	76	282
Acquired Loans [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	525	1,591
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial non-real estate	59,843	120,137
Current	59,843	120,137
Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Construction and land development	5,080	21,123
Total past due		111
Current	5,080	21,012
Acquired Loans [Member] | Construction and Land Development [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		111
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial real estate	176,460	688,045
Total past due	616	5,734
Current	175,844	682,311
Recorded investment > 90 days and accruing		261
Acquired Loans [Member] | Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	15	3,861
Acquired Loans [Member] | Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	76	282
Acquired Loans [Member] | Commercial Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due	525	1,591
Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Residential mortgages	27	2,378
Current	27	2,378
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Consumer	20	985
Current	20	985
FDIC Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	203,297	252,409
Total past due		1,843
Current	203,297	250,566
FDIC Acquired Loans [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1
FDIC Acquired Loans [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		272
FDIC Acquired Loans [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1,570
FDIC Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	5,528	6,195
Current	5,528	6,195
FDIC Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	7,127	11,674
Total past due		1,103
Current	7,127	10,571
FDIC Acquired Loans [Member] | Construction and Land Development [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1,103
FDIC Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	15,582	27,808
Total past due		433
Current	15,582	27,375
FDIC Acquired Loans [Member] | Commercial Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		433
FDIC Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	162,241	187,033
Total past due		272
Current	162,241	186,761
FDIC Acquired Loans [Member] | Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		272
FDIC Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	12,819	19,699
Total past due		35
Current	$ 12,819	19,664
FDIC Acquired Loans [Member] | Consumer [Member] | 30-59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		1
FDIC Acquired Loans [Member] | Consumer [Member] | Greater Than 90 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total past due		$ 34