Loans - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 199,611	$ 306,426
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	168,854	284,409
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	4,666	4,627
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	26,091	17,390
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	1,584,250	1,841,465
Accruing	10,150	4,249
Non-accrual Loans	14,208	6,958
Discount/Premium	(10,629)	(12,811)
Acquired Impaired Loans	464,627	530,186
Total Loans	2,062,606	2,370,047
Acquired Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total Loans	1,321,861	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	53,564	26,714
Accruing	216	0
Non-accrual Loans	1,118	1,946
Discount/Premium	(183)	(243)
Acquired Impaired Loans	34,994	32,991
Total Loans	89,709	61,408
Acquired Loans | Commercial Loans | Commercial real estate- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	284,841	326,761
Accruing	0	548
Non-accrual Loans	3,684	166
Discount/Premium	(2,670)	(3,084)
Acquired Impaired Loans	104,386	125,621
Total Loans	390,241	450,012
Acquired Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	441,193	544,731
Accruing	2,386	255
Non-accrual Loans	4,035	1,055
Discount/Premium	(94)	(565)
Acquired Impaired Loans	99,203	122,056
Total Loans	546,723	667,532
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	256,584	314,990
Accruing	4,698	124
Non-accrual Loans	1,382	1,317
Discount/Premium	(712)	(837)
Acquired Impaired Loans	31,430	32,732
Total Loans	293,382	348,326
Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Current or Less Than 30 days past due	1,657	1,910
Accruing	154	0
Non-accrual Loans	0	0
Discount/Premium	(5)	(6)
Acquired Impaired Loans	0	0
Total Loans	1,806	1,904
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	378,204	424,300
Current or Less Than 30 days past due	263,658	290,031
Accruing	609	1,317
Non-accrual Loans	1,598	719
Discount/Premium	(1,609)	(1,835)
Acquired Impaired Loans	111,250	122,952
Total Loans	375,506	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	322,658	377,021
Current or Less Than 30 days past due	242,091	286,411
Accruing	1,686	1,517
Non-accrual Loans	1,947	1,395
Discount/Premium	(4,497)	(5,237)
Acquired Impaired Loans	78,880	88,419
Total Loans	320,107	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	24	12
Current or Less Than 30 days past due	18	0
Accruing	0	0
Non-accrual Loans	0	0
Discount/Premium	0	0
Acquired Impaired Loans	6	4
Total Loans	24	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	40,644	49,449
Accruing	401	488
Non-accrual Loans	444	360
Discount/Premium	(859)	(1,004)
Acquired Impaired Loans	3,977	5,411
Total Loans	44,607	54,704
Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	13,288,170	12,447,375
Accruing	41,492	26,006
Non-accrual Loans	163,748	221,543
Total Loans	13,493,410	12,694,924
Legacy Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total Loans	10,055,791	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	1,008,834	740,761
Accruing	214	0
Non-accrual Loans	1,431	0
Total Loans	1,010,479	740,761
Legacy Loans | Commercial Loans | Commercial real estate- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	1,804,289	1,775,695
Accruing	2,063	1,086
Non-accrual Loans	8,815	7,843
Total Loans	1,815,167	1,784,624
Legacy Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	3,277,719	3,088,207
Accruing	6,558	1,126
Non-accrual Loans	5,007	8,596
Total Loans	3,289,284	3,097,929
Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	3,349,442	3,158,700
Accruing	12,062	4,869
Non-accrual Loans	29,195	31,227
Total Loans	3,390,699	3,194,796
Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	453,357	407,434
Accruing	2,240	1,526
Non-accrual Loans	94,565	150,329
Total Loans	550,162	559,289
Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	955,343	836,509
Accruing	3,936	4,693
Non-accrual Loans	11,682	13,014
Total Loans	970,961	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	1,819,163	1,768,763
Accruing	9,144	6,679
Non-accrual Loans	10,534	7,979
Total Loans	1,838,841	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	89,590	127,054
Accruing	1,614	2,956
Non-accrual Loans	902	1,038
Total Loans	92,106	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	85,690	81,602
Accruing	285	298
Non-accrual Loans	612	624
Total Loans	86,587	82,524
Legacy Loans | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Current or less than 30 days past due	444,743	462,650
Accruing	3,376	2,773
Non-accrual Loans	1,005	893
Total Loans	449,124	466,316
30-59 days | Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	3,212	2,586
30-59 days | Acquired Loans | Commercial Loans | Commercial real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	216	0
30-59 days | Acquired Loans | Commercial Loans | Commercial real estate- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	493
30-59 days | Acquired Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,067	223
30-59 days | Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	47	73
30-59 days | Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	154	0
30-59 days | Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	14	328
30-59 days | Acquired Loans | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	407	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	307	391
30-59 days | Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	27,921	18,026
30-59 days | Legacy Loans | Commercial Loans | Commercial real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	214	0
30-59 days | Legacy Loans | Commercial Loans | Commercial real estate- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	343	959
30-59 days | Legacy Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,245	902
30-59 days | Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	10,633	3,999
30-59 days | Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	2,240	0
30-59 days | Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	1,933	2,012
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	4,983	5,249
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	1,353	2,551
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	168	199
30-59 days | Legacy Loans | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Accruing	2,809	2,155
60-89 days | Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	6,746	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- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	55
60-89 days | Acquired Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	319	0
60-89 days | Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	4,651	51
60-89 days | Acquired Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	403	989
60-89 days | Acquired Loans | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	1,279	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	94	97
60-89 days | Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	12,961	6,876
60-89 days | Legacy Loans | Commercial Loans | Commercial real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Legacy Loans | Commercial Loans | Commercial real estate- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	1,687	127
60-89 days | Legacy Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,046	224
60-89 days | Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	1,429	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	1,693	1,577
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	4,161	1,430
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	261	405
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	117	99
60-89 days | Legacy Loans | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Accruing	567	618
Greater than 90 days | Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	192	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- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Acquired Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	32
Greater than 90 days | Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	0	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	192	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	610	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- owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	33	0
Greater than 90 days | Legacy Loans | Commercial Loans | Commercial real estate- non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	267	0
Greater than 90 days | Legacy Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans | Commercial Loans | Energy-related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Legacy Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	310	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	$ 0	$ 0