Loans - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 257,825	$ 306,426
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	228,981	284,409
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	4,911	4,627
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	23,933	17,390
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	1,707,845	1,841,465
Accruing	8,766	4,249
Non-accrual Loans	6,504	6,958
Discount/Premium	(11,696)	(12,811)
Acquired Impaired Loans	497,339	530,186
Total Loans	2,208,758	2,370,047
Acquired Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total Loans	1,415,846	1,529,182
Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	25,425	26,714
Accruing	0	0
Non-accrual Loans	1,946	1,946
Discount/Premium	(202)	(243)
Acquired Impaired Loans	34,787	32,991
Total Loans	61,956	61,408
Acquired Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	811,160	871,492
Accruing	3,998	803
Non-accrual Loans	957	1,221
Discount/Premium	(3,258)	(3,649)
Acquired Impaired Loans	224,552	247,677
Total Loans	1,037,409	1,117,544
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	280,869	314,990
Accruing	1,594	124
Non-accrual Loans	1,101	1,317
Discount/Premium	(745)	(837)
Acquired Impaired Loans	32,554	32,732
Total Loans	315,373	348,326
Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	956	1,910
Accruing	157	0
Non-accrual Loans	0	0
Discount/Premium	(5)	(6)
Acquired Impaired Loans	0	0
Total Loans	1,108	1,904
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	404,276	424,300
Current or Less Than 30 days past due	278,684	290,031
Accruing	1,462	1,317
Non-accrual Loans	789	719
Discount/Premium	(1,729)	(1,835)
Acquired Impaired Loans	115,293	122,952
Total Loans	394,499	413,184
Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	352,836	377,021
Current or Less Than 30 days past due	266,706	286,411
Accruing	1,300	1,517
Non-accrual Loans	1,367	1,395
Discount/Premium	(4,826)	(5,237)
Acquired Impaired Loans	85,126	88,419
Total Loans	349,673	372,505
Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	26	12
Current or Less Than 30 days past due	19	0
Accruing	0	0
Non-accrual Loans	0	0
Discount/Premium	0	0
Acquired Impaired Loans	7	4
Total Loans	26	4
Acquired Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	0	468
Accruing	0	0
Non-accrual Loans	0	0
Discount/Premium	0	0
Acquired Impaired Loans	501	0
Total Loans	501	468
Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	44,026	49,449
Accruing	255	488
Non-accrual Loans	344	360
Discount/Premium	(931)	(1,004)
Acquired Impaired Loans	4,519	5,411
Total Loans	48,213	54,704
Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	12,702,980	12,447,375
Accruing	35,386	26,006
Non-accrual Loans	185,078	221,543
Total Loans	12,923,444	12,694,924
Legacy Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total Loans	9,581,229	9,377,399
Legacy Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	880,721	740,761
Accruing	1,618	0
Non-accrual Loans	0	0
Total Loans	882,339	740,761
Legacy Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	4,973,144	4,863,902
Accruing	5,555	2,212
Non-accrual Loans	17,471	16,439
Total Loans	4,996,170	4,882,553
Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	3,102,314	3,158,700
Accruing	6,996	4,869
Non-accrual Loans	30,895	31,227
Total Loans	3,140,205	3,194,796
Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	447,128	407,434
Accruing	2,175	1,526
Non-accrual Loans	113,212	150,329
Total Loans	562,515	559,289
Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	884,571	836,509
Accruing	4,320	4,693
Non-accrual Loans	12,968	13,014
Total Loans	901,859	854,216
Legacy Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	1,779,409	1,768,763
Accruing	9,813	6,679
Non-accrual Loans	7,901	7,979
Total Loans	1,797,123	1,783,421
Legacy Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	107,519	127,054
Accruing	1,632	2,956
Non-accrual Loans	1,023	1,038
Total Loans	110,174	131,048
Legacy Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	82,636	81,602
Accruing	540	298
Non-accrual Loans	436	624
Total Loans	83,612	82,524
Legacy Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	445,538	462,650
Accruing	2,737	2,773
Non-accrual Loans	1,172	893
Total Loans	449,447	466,316
30-59 days | Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	2,502	2,586
30-59 days | Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
30-59 days | Acquired Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	0	716
30-59 days | Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	287	73
30-59 days | Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
30-59 days | Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	919	328
30-59 days | Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	1,078	1,078
30-59 days | Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
30-59 days | Acquired Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
30-59 days | Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	218	391
30-59 days | Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	25,402	18,026
30-59 days | Legacy Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	187	0
30-59 days | Legacy Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	4,432	1,861
30-59 days | Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	6,399	3,999
30-59 days | Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
30-59 days | Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	2,692	2,012
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	7,868	5,249
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	1,333	2,551
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	350	199
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	2,141	2,155
60-89 days | Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	1,384	1,381
60-89 days | Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Acquired Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	314	55
60-89 days | Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	111	51
60-89 days | Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	157	0
60-89 days | Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	543	989
60-89 days | Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	222	189
60-89 days | Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Acquired Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	37	97
60-89 days | Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	6,884	6,876
60-89 days | Legacy Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	1,431	0
60-89 days | Legacy Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	586	351
60-89 days | Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	224	870
60-89 days | Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	1,526
60-89 days | Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	1,628	1,577
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	1,945	1,430
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	299	405
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	190	99
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	581	618
Greater than 90 days | Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	4,880	282
Greater than 90 days | Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Acquired Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	3,684	32
Greater than 90 days | Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	1,196	0
Greater than 90 days | Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	0	250
Greater than 90 days | Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Acquired Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	3,100	1,104
Greater than 90 days | Legacy Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans | Commercial Loans | Commercial real estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	537	0
Greater than 90 days | Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	373	0
Greater than 90 days | Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	2,175	0
Greater than 90 days | Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	0	1,104
Greater than 90 days | Legacy Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 15	$ 0