Loans - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 86,581	$ 68,617
Non-accrual Loans	153,975	145,388
Acquired Impaired Loans	196,532	238,127
Total Loans	21,706,090	20,078,181
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	157,214	194,201
Total Loans	14,574,633	14,073,297
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	971	727
Non-accrual Loans	2,634	2,635
Total Loans	1,199,625	1,240,396
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	8,228	2,364
Non-accrual Loans	35,144	24,457
Total Loans	2,612,244	2,529,885
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	16,584	9,378
Non-accrual Loans	9,378	6,811
Total Loans	5,437,082	5,167,949
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	11,434	11,660
Non-accrual Loans	66,637	77,823
Total Loans	5,325,682	5,135,067
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	6,041	6,749
Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	3,859,751	2,962,043
Accruing	29,521	23,536
Non-accrual Loans	19,932	17,387
Total Loans	3,971,067	3,056,352
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	33,277	37,177
Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,376,171	2,250,205
Accruing	15,051	14,640
Non-accrual Loans	16,383	12,365
Total Loans	2,421,186	2,292,275
Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current	48,587	59,836
Accruing	1,341	1,973
Non-accrual Loans	743	884
Total Loans	50,671	62,693
Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current	92,497	95,263
Accruing	261	514
Non-accrual Loans	503	590
Total Loans	93,261	96,368
Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	589,098	490,399
Accruing	3,190	3,825
Non-accrual Loans	2,621	2,436
Total Loans	595,272	497,196
Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Current	20,983,656	19,382,621
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current	1,157,115	1,197,766
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	2,474,611	2,398,487
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	5,319,962	5,066,084
Current or Less Than 30 days past due | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current	5,212,390	5,014,438
Current or Less Than 30 days past due | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	3,783,309	2,877,048
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,309,222	2,186,554
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Current	48,581	59,830
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Current	92,497	95,264
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	585,969	487,150
30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	61,956	36,818
30-59 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	842	269
30-59 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	4,767	1,631
30-59 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	7,269	2,086
30-59 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	7,755	5,788
30-59 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	25,640	10,083
30-59 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	11,860	11,675
30-59 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	1,166	1,796
30-59 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	173	140
30-59 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	2,484	3,350
60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	16,337	24,899
60-89 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	129	0
60-89 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,461	659
60-89 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,526	6,405
60-89 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	3,406	5,726
60-89 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	2,655	8,136
60-89 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	3,191	2,947
60-89 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	175	177
60-89 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	88	374
60-89 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	706	475
Greater than 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	8,288	6,900
Greater than 90 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	458
Greater than 90 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	74
Greater than 90 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	6,789	887
Greater than 90 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	273	146
Greater than 90 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	1,226	5,317
Greater than 90 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	0	18
Greater than 90 days | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	481,878	481,555
Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	38,905	39,268
Acquired Loans | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	94,261	104,577
Acquired Loans | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	91,158	85,676
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	35,221	31,146
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	138,305	138,381
Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	80,530	78,716
Acquired Loans | Consumer and Other Loans | Consumer - Indirect automobile
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	6	6
Acquired Loans | Consumer and Other Loans | Consumer - Credit card
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	0	0
Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 3,492	$ 3,785