Loans - Schedule of Aging of Non-Covered Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 356,021	$ 102,733
Total Loans	14,722,288	14,098,211
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	315,357	73,846
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	18,205	14,806
Consumer
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	22,459	14,081
Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	46,093	20,733
Non-accrual Loans	227,122	50,928
Total Loans	12,413,370	11,190,520
Legacy Loans | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	12,140,155	11,118,859
Legacy Loans | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	28,437	13,839
Legacy Loans | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	12,720	6,270
Legacy Loans | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	4,936	624
Legacy Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total Loans	9,119,234	8,133,341
Legacy Loans | Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	1,234	801
Non-accrual Loans	25	120
Total Loans	696,127	636,481
Legacy Loans | Commercial Loans | Commercial Real Estate - Construction | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	694,868	635,560
Legacy Loans | Commercial Loans | Commercial Real Estate - Construction | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	801
Legacy Loans | Commercial Loans | Commercial Real Estate - Construction | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Legacy Loans | Commercial Loans | Commercial Real Estate - Construction | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,234	0
Legacy Loans | Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	4,348	3,575
Non-accrual Loans	14,920	15,422
Total Loans	4,723,356	3,867,581
Legacy Loans | Commercial Loans | Commercial Real Estate - Other | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	4,704,088	3,848,584
Legacy Loans | Commercial Loans | Commercial Real Estate - Other | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,514	2,687
Legacy Loans | Commercial Loans | Commercial Real Estate - Other | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	445	793
Legacy Loans | Commercial Loans | Commercial Real Estate - Other | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	2,389	95
Legacy Loans | Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	16,265	2,034
Non-accrual Loans	34,966	6,659
Total Loans	3,101,472	2,952,102
Legacy Loans | Commercial Loans | Commercial and Industrial | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	3,050,241	2,943,409
Legacy Loans | Commercial Loans | Commercial and Industrial | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	14,713	1,208
Legacy Loans | Commercial Loans | Commercial and Industrial | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,404	739
Legacy Loans | Commercial Loans | Commercial and Industrial | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	148	87
Legacy Loans | Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	15
Non-accrual Loans	153,620	7,081
Total Loans	598,279	677,177
Legacy Loans | Commercial Loans | Energy-Related | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	444,659	670,081
Legacy Loans | Commercial Loans | Energy-Related | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	15
Legacy Loans | Commercial Loans | Energy-Related | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Legacy Loans | Commercial Loans | Energy-Related | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Legacy Loans | Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	9,112	4,002
Non-accrual Loans	13,816	13,674
Total Loans	840,082	694,023
Legacy Loans | Residential Mortgage Loans | Residential Mortgage | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	817,154	676,347
Legacy Loans | Residential Mortgage Loans | Residential Mortgage | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,396	1,075
Legacy Loans | Residential Mortgage Loans | Residential Mortgage | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	7,389	2,485
Legacy Loans | Residential Mortgage Loans | Residential Mortgage | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	327	442
Legacy Loans | Consumer | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Accruing	8,276	4,419
Non-accrual Loans	7,018	5,628
Total Loans	1,755,295	1,575,643
Legacy Loans | Consumer | Consumer - Home Equity | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	1,740,001	1,565,596
Legacy Loans | Consumer | Consumer - Home Equity | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	6,207	3,549
Legacy Loans | Consumer | Consumer - Home Equity | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,968	870
Legacy Loans | Consumer | Consumer - Home Equity | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	101	0
Legacy Loans | Consumer | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	2,556	2,705
Non-accrual Loans	1,340	1,181
Total Loans	153,904	246,214
Legacy Loans | Consumer | Consumer - Indirect Automobile | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	150,008	242,328
Legacy Loans | Consumer | Consumer - Indirect Automobile | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	2,151	2,187
Legacy Loans | Consumer | Consumer - Indirect Automobile | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	405	518
Legacy Loans | Consumer | Consumer - Indirect Automobile | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Legacy Loans | Consumer | Consumer - Credit Card
Accounts, Notes, Loans and Financing Receivable
Accruing	426	507
Non-accrual Loans	438	394
Total Loans	80,452	77,261
Legacy Loans | Consumer | Consumer - Credit Card | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	79,588	76,360
Legacy Loans | Consumer | Consumer - Credit Card | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	311	394
Legacy Loans | Consumer | Consumer - Credit Card | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	115	113
Legacy Loans | Consumer | Consumer - Credit Card | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Legacy Loans | Consumer | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	3,876	2,675
Non-accrual Loans	979	769
Total Loans	464,403	464,038
Legacy Loans | Consumer | Consumer - Other | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	459,548	460,594
Legacy Loans | Consumer | Consumer - Other | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	2,145	1,923
Legacy Loans | Consumer | Consumer - Other | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	994	752
Legacy Loans | Consumer | Consumer - Other | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	737	0
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Accruing	4,265	5,357
Non-accrual Loans	8,399	5,421
Discount/Premium	(18,363)	(23,856)
Acquired Impaired Loans	569,047	724,719
Total Loans	2,511,129	3,136,908
Acquired Loans | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	1,947,781	2,425,267
Acquired Loans | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,501	2,761
Acquired Loans | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	2,467	2,305
Acquired Loans | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	297	291
Acquired Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Total Loans	1,624,619	2,065,514
Acquired Loans | Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	297
Non-accrual Loans	1,946	0
Discount/Premium	(285)	(358)
Acquired Impaired Loans	37,516	56,320
Total Loans	80,795	125,426
Acquired Loans | Commercial Loans | Commercial Real Estate - Construction | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	41,618	69,167
Acquired Loans | Commercial Loans | Commercial Real Estate - Construction | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	180
Acquired Loans | Commercial Loans | Commercial Real Estate - Construction | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	117
Acquired Loans | Commercial Loans | Commercial Real Estate - Construction | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	387	1,566
Non-accrual Loans	1,976	1,491
Discount/Premium	(4,991)	(4,479)
Acquired Impaired Loans	270,046	354,757
Total Loans	1,180,937	1,444,023
Acquired Loans | Commercial Loans | Commercial Real Estate - Other | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	913,519	1,090,688
Acquired Loans | Commercial Loans | Commercial Real Estate - Other | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	861
Acquired Loans | Commercial Loans | Commercial Real Estate - Other | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	387	705
Acquired Loans | Commercial Loans | Commercial Real Estate - Other | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	810	623
Non-accrual Loans	1,770	1,154
Discount/Premium	(705)	(2,517)
Acquired Impaired Loans	35,154	50,762
Total Loans	361,525	492,476
Acquired Loans | Commercial Loans | Commercial and Industrial | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	324,496	442,454
Acquired Loans | Commercial Loans | Commercial and Industrial | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	561	623
Acquired Loans | Commercial Loans | Commercial and Industrial | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	249	0
Acquired Loans | Commercial Loans | Commercial and Industrial | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Non-accrual Loans	0	170
Discount/Premium	(7)	2
Acquired Impaired Loans	0	1,231
Total Loans	1,362	3,589
Acquired Loans | Commercial Loans | Energy-Related | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	1,369	2,186
Acquired Loans | Commercial Loans | Energy-Related | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Commercial Loans | Energy-Related | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Commercial Loans | Energy-Related | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	1,619	947
Non-accrual Loans	1,258	1,109
Discount/Premium	(5,855)	(6,601)
Acquired Impaired Loans	125,749	140,580
Total Loans	430,448	501,296
Acquired Loans | Residential Mortgage Loans | Residential Mortgage | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	307,677	365,261
Acquired Loans | Residential Mortgage Loans | Residential Mortgage | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	7
Acquired Loans | Residential Mortgage Loans | Residential Mortgage | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	1,339	940
Acquired Loans | Residential Mortgage Loans | Residential Mortgage | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	280	0
Acquired Loans | Consumer | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Accruing	725	1,329
Non-accrual Loans	1,206	1,291
Discount/Premium	(1,762)	(7,333)
Acquired Impaired Loans	94,502	114,130
Total Loans	395,835	490,524
Acquired Loans | Consumer | Consumer - Home Equity | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	301,164	381,107
Acquired Loans | Consumer | Consumer - Home Equity | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	419	622
Acquired Loans | Consumer | Consumer - Home Equity | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	289	416
Acquired Loans | Consumer | Consumer - Home Equity | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	17	291
Acquired Loans | Consumer | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Non-accrual Loans	0	0
Discount/Premium	0	0
Acquired Impaired Loans	0	65
Total Loans	9	84
Acquired Loans | Consumer | Consumer - Indirect Automobile | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	9	19
Acquired Loans | Consumer | Consumer - Indirect Automobile | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Indirect Automobile | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Indirect Automobile | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Credit Card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Non-accrual Loans	0	0
Discount/Premium	0	0
Acquired Impaired Loans	507	582
Total Loans	507	582
Acquired Loans | Consumer | Consumer - Credit Card | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Credit Card | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Credit Card | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Credit Card | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans | Consumer | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	724	595
Non-accrual Loans	243	206
Discount/Premium	(4,758)	(2,570)
Acquired Impaired Loans	5,573	6,292
Total Loans	59,711	78,908
Acquired Loans | Consumer | Consumer - Other | Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Accruing	57,929	74,385
Acquired Loans | Consumer | Consumer - Other | 30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	521	468
Acquired Loans | Consumer | Consumer - Other | 60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	203	127
Acquired Loans | Consumer | Consumer - Other | 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 0	$ 0