Loans and Allowance for Loan Losses - Summary of Age Analysis of Past Due Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	$ 224,637	$ 252,409
Total loans	14,344,752	13,895,276
30-59 days past due	24,268	44,652
60-89 days past due	13,585	12,503
Greater than 90 days past due	43,871	44,981
Total past due	81,724	102,136
Current	14,263,028	13,793,140
Recorded investment > 90 days and accruing	3,478	4,825
Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	6,666	6,195
Total loans	6,185,684	6,044,060
30-59 days past due	5,215	4,380
60-89 days past due	3,090	1,742
Greater than 90 days past due	10,250	8,560
Total past due	18,555	14,682
Current	6,167,129	6,029,378
Recorded investment > 90 days and accruing	826	630
Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	11,095	11,674
Total loans	1,120,947	1,106,761
30-59 days past due	2,411	6,731
60-89 days past due	2,128	1,532
Greater than 90 days past due	5,434	5,556
Total past due	9,973	13,819
Current	1,110,974	1,092,942
Recorded investment > 90 days and accruing	80	142
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	22,487	27,808
Total loans	3,212,833	3,144,048
30-59 days past due	5,134	10,388
60-89 days past due	1,588	3,246
Greater than 90 days past due	16,732	15,258
Total past due	23,454	28,892
Current	3,189,379	3,115,156
Recorded investment > 90 days and accruing	279	957
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	169,553	187,033
Total loans	1,955,837	1,894,181
30-59 days past due	1,094	14,730
60-89 days past due	3,493	3,533
Greater than 90 days past due	8,227	11,208
Total past due	12,814	29,471
Current	1,943,023	1,864,710
Recorded investment > 90 days and accruing	946	1,199
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total FDIC acquired loans	14,836	19,699
Total loans	1,869,451	1,706,226
30-59 days past due	10,414	8,423
60-89 days past due	3,286	2,450
Greater than 90 days past due	3,228	4,399
Total past due	16,928	15,272
Current	1,852,523	1,690,954
Recorded investment > 90 days and accruing	1,347	1,897
Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	13,390,491	12,810,199
30-59 days past due	22,314	40,679
60-89 days past due	13,447	11,949
Greater than 90 days past due	40,250	41,820
Total past due	76,011	94,448
Current	13,314,480	12,715,751
Recorded investment > 90 days and accruing	3,478	4,564
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial non-real estate	6,058,998	5,917,728
30-59 days past due	5,215	4,380
60-89 days past due	3,090	1,742
Greater than 90 days past due	10,250	8,560
Total past due	18,555	14,682
Current	6,040,443	5,903,046
Recorded investment > 90 days and accruing	826	630
Originated Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Construction and land development	1,100,788	1,073,964
30-59 days past due	2,411	6,620
60-89 days past due	2,128	1,532
Greater than 90 days past due	4,278	4,453
Total past due	8,817	12,605
Current	1,091,971	1,061,359
Recorded investment > 90 days and accruing	80	142
Originated Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial real estate	2,591,384	2,428,195
30-59 days past due	3,180	6,527
60-89 days past due	1,450	2,964
Greater than 90 days past due	14,267	13,234
Total past due	18,897	22,725
Current	2,572,487	2,405,470
Recorded investment > 90 days and accruing	279	696
Originated Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Residential mortgages	1,784,730	1,704,770
30-59 days past due	1,094	14,730
60-89 days past due	3,493	3,261
Greater than 90 days past due	8,227	11,208
Total past due	12,814	29,199
Current	1,771,916	1,675,571
Recorded investment > 90 days and accruing	946	1,199
Originated Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Consumer	1,854,591	1,685,542
30-59 days past due	10,414	8,422
60-89 days past due	3,286	2,450
Greater than 90 days past due	3,228	4,365
Total past due	16,928	15,237
Current	1,837,663	1,670,305
Recorded investment > 90 days and accruing	1,347	1,897
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	729,624	832,668
30-59 days past due	1,954	3,972
60-89 days past due	138	282
Greater than 90 days past due	2,032	1,591
Total past due	4,124	5,845
Current	725,500	826,823
Recorded investment > 90 days and accruing		261
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial non-real estate	120,020	120,137
Current	120,020	120,137
Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Construction and land development	9,064	21,123
30-59 days past due		111
Total past due		111
Current	9,064	21,012
Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial real estate	598,962	688,045
30-59 days past due	1,954	3,861
60-89 days past due	138	282
Greater than 90 days past due	2,032	1,591
Total past due	4,124	5,734
Current	594,838	682,311
Recorded investment > 90 days and accruing		261
Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Residential mortgages	1,554	2,378
Current	1,554	2,378
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Consumer	24	985
Current	24	985
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	1,589	1,570
Total past due	1,589	1,843
Current	223,048	250,566
FDIC Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current	6,666	6,195
FDIC Acquired Loans [Member] | Construction and Land Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	1,156	1,103
Total past due	1,156	1,103
Current	9,939	10,571
FDIC Acquired Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Greater than 90 days past due	433	433
Total past due	433	433
Current	22,054	27,375
FDIC Acquired Loans [Member] | Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
60-89 days past due		272
Total past due		272
Current	169,553	186,761
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	$ 14,836	$ 19,664