Loans and Leases - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 49,445	$ 59,460
Non-accrual Loans	148,056	137,184
Acquired Impaired Loans	175,312	169,725
Total Loans	22,968,295	22,519,815
Financing Receivable, Nonaccrual Loans, Thirty To Fifty-Nine Days Past Due, Amount	9,000	7,000
Financing Receivable, Nonaccrual Loans, Sixty to Eighty-Nine Days Past Due, Amount	4,600	3,700
Financing Receivable, Nonacrrual Loans, Over Ninety Days Past Due, Amount	53,700	66,900
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	131,798	125,706
Total Loans	15,628,158	15,125,322
Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	305	1,054
Non-accrual Loans	1,072	1,094
Total Loans	1,219,647	1,196,366
Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	5,716	7,167
Non-accrual Loans	8,630	10,260
Total Loans	2,408,079	2,395,822
Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,167	7,833
Non-accrual Loans	19,984	15,898
Total Loans	6,147,864	5,796,117
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	9,715	7,012
Non-accrual Loans	51,447	57,860
Total Loans	5,852,568	5,737,017
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	7,679	6,579
Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	4,335,779	4,290,152
Accruing	15,640	17,406
Non-accrual Loans	45,473	30,396
Total Loans	4,415,267	4,359,156
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	35,835	37,440
Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,184,204	2,258,659
Accruing	11,689	12,692
Non-accrual Loans	18,719	18,830
Total Loans	2,220,648	2,304,694
Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	698,074	721,231
Accruing	3,213	6,296
Non-accrual Loans	2,731	2,846
Total Loans	704,222	730,643
Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Current	22,442,552	21,959,758
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Current	1,197,063	1,167,795
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	2,324,441	2,305,743
Current or Less Than 30 days past due | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	6,054,340	5,703,131
Current or Less Than 30 days past due | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current	5,766,811	5,645,304
Current or Less Than 30 days past due | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	4,269,617	4,218,146
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Current	2,134,340	2,200,517
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Current	695,940	719,122
30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	36,607	38,579
30-59 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	305	1,054
30-59 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,510	7,167
30-59 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,213	7,473
30-59 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	8,881	5,139
30-59 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	10,884	2,768
30-59 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	9,511	10,283
30-59 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	2,303	4,695
60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	8,727	18,753
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	67	0
60-89 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	91	360
60-89 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	725	1,320
60-89 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	4,756	13,063
60-89 days | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	2,178	2,409
60-89 days | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Accruing	910	1,601
Greater than 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	4,111	2,128
Greater than 90 days | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	3,139	0
Greater than 90 days | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	863	0
Greater than 90 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	109	553
Greater than 90 days | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	0	1,575
Greater than 90 days | Consumer and Other Loans | Consumer - Home equity
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	328,242	363,413
Acquired Loans | Commercial Loans | Commercial real estate - Construction
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	21,207	26,423
Acquired Loans | Commercial Loans | Commercial real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	69,292	72,652
Acquired Loans | Commercial Loans | Commercial real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	70,373	69,255
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	24,595	26,841
Acquired Loans | Residential Mortgage | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	84,537	93,208
Acquired Loans | Consumer and Other Loans | Consumer - Home equity
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	55,900	72,655
Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	$ 2,338	$ 2,379