Loans and Leases - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 52,473	$ 68,617
Non-accrual Loans	131,155	145,388
Acquired Impaired Loans	192,323	238,127
Total Loans	22,075,783	20,078,181
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	150,900	194,201
Total Loans	14,804,720	14,073,297
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	698	727
Non-accrual Loans	1,164	2,635
Total Loans	1,183,367	1,240,396
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,704	2,364
Non-accrual Loans	27,730	24,457
Total Loans	2,641,824	2,529,885
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	4,588	9,378
Non-accrual Loans	10,409	6,811
Total Loans	5,467,113	5,167,949
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	7,616	11,660
Non-accrual Loans	60,741	77,823
Total Loans	5,512,416	5,135,067
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	5,873	6,749
Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	4,033,339	2,962,043
Accruing	20,219	23,536
Non-accrual Loans	13,066	17,387
Total Loans	4,124,538	3,056,352
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	35,550	37,177
Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,367,409	2,250,205
Accruing	11,046	14,640
Non-accrual Loans	15,369	12,365
Total Loans	2,410,617	2,292,275
Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	728,263	645,498
Accruing	4,602	6,312
Non-accrual Loans	2,676	3,910
Total Loans	735,908	656,257
Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Current	21,454,657	19,382,621
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current	1,161,597	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	2,521,815	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	5,370,268	5,066,084
Current or Less Than 30 days past due | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current	5,413,419	5,014,438
Current or Less Than 30 days past due | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	3,956,674	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	2,305,534	2,186,554
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	725,350	642,244
30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	27,674	36,818
30-59 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	698	269
30-59 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	1,644	1,631
30-59 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	4,086	2,086
30-59 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	3,944	5,788
30-59 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	5,274	10,083
30-59 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	8,175	11,675
30-59 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	3,853	5,286
60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	15,485	24,899
60-89 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	1,840	659
60-89 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	502	6,405
60-89 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	2,944	5,726
60-89 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	7,029	8,136
60-89 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	2,421	2,947
60-89 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	749	1,026
Greater than 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	9,314	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	220	74
Greater than 90 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	0	887
Greater than 90 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	728	146
Greater than 90 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	7,916	5,317
Greater than 90 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	450	18
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	437,498	481,555
Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	19,908	39,268
Acquired Loans | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	88,575	104,577
Acquired Loans | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	81,848	85,676
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	30,640	31,146
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	134,579	138,381
Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	78,668	78,716
Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 3,280	$ 3,791