Loans and Allowance for Loan Losses - Schedule of Credit Quality Indicators of Various Classes of Loans - Credit Risk Profile by Internally Assigned Grade (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	$ 1,120,947	$ 1,106,761
Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	6,185,684	6,044,060
Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,212,833	3,144,048
Originated Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,100,788	1,073,964
Originated Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	6,058,998	5,917,728
Originated Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,591,384	2,428,195
Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	9,064	21,123
Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	120,020	120,137
Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	598,962	688,045
FDIC Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	11,095	11,674
FDIC Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	6,666	6,195
FDIC Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	22,487	27,808
Pass [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,052,912	1,028,973
Pass [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,638,084	5,691,701
Pass [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,001,533	2,887,496
Pass [Member] | Originated Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,048,380	1,012,128
Pass [Member] | Originated Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,522,236	5,577,827
Pass [Member] | Originated Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,430,696	2,241,391
Pass [Member] | Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,743	14,377
Pass [Member] | Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	113,200	111,847
Pass [Member] | Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	565,820	641,966
Pass [Member] | FDIC Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,789	2,468
Pass [Member] | FDIC Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,648	2,027
Pass [Member] | FDIC Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,017	4,139
Pass-Watch [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	10,265	22,480
Pass-Watch [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	143,926	176,577
Pass-Watch [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	46,966	77,278
Pass-Watch [Member] | Originated Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	7,471	21,516
Pass-Watch [Member] | Originated Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	142,837	174,742
Pass-Watch [Member] | Originated Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	33,185	61,589
Pass-Watch [Member] | Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,275	432
Pass-Watch [Member] | Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	101	715
Pass-Watch [Member] | Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	10,974	11,142
Pass-Watch [Member] | FDIC Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	519	532
Pass-Watch [Member] | FDIC Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	988	1,120
Pass-Watch [Member] | FDIC Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,807	4,547
Special Mention [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,233	7,545
Special Mention [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	209,998	53,312
Special Mention [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	33,381	30,975
Special Mention [Member] | Originated Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	4,920	7,097
Special Mention [Member] | Originated Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	209,716	52,962
Special Mention [Member] | Originated Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	25,974	21,543
Special Mention [Member] | Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade		129
Special Mention [Member] | Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	282	350
Special Mention [Member] | Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,798	8,113
Special Mention [Member] | FDIC Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	313	319
Special Mention [Member] | FDIC Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,609	1,319
Substandard [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	52,537	47,763
Substandard [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	193,616	122,395
Substandard [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	130,936	148,278
Substandard [Member] | Originated Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	40,017	33,223
Substandard [Member] | Originated Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	184,178	112,153
Substandard [Member] | Originated Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	101,512	103,651
Substandard [Member] | Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,046	6,185
Substandard [Member] | Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	6,437	7,225
Substandard [Member] | Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	16,370	26,824
Substandard [Member] | FDIC Acquired Loans [Member] | Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	7,474	8,355
Substandard [Member] | FDIC Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	3,001	3,017
Substandard [Member] | FDIC Acquired Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	13,054	17,803
Doubtful [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	60	75
Doubtful [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	17	21
Doubtful [Member] | Originated Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	31	44
Doubtful [Member] | Originated Loans [Member] | Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	17	21
Doubtful [Member] | FDIC Acquired Loans [Member] | Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	$ 29	$ 31