Loans and Leases - Schedule of Aging of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Accruing	$ 71,461	$ 59,460
Non-accrual Loans	138,905	137,184
Acquired Impaired Loans	188,274	169,725	$ 238,127
Total Loans	24,021,499	22,519,815
Non-accrual loans past due, 30-59 days	8,700	7,000
Non-accrual loan past due, 60-89 days	4,300	3,700
Non-accrual loans past due, more than 90 days	73,200	66,900
Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	118,653	125,706	194,201
Total Loans	16,611,633	15,125,322
Commercial Loans | Real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	244	1,054
Non-accrual Loans	1,394	1,094
Total Loans	1,321,663	1,196,366
Commercial Loans | Real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	17,772	7,167
Non-accrual Loans	17,817	10,260
Total Loans	2,475,326	2,395,822
Commercial Loans | Real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	5,348	7,833
Non-accrual Loans	15,440	15,898
Total Loans	6,267,106	5,796,117
Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	8,427	7,012
Non-accrual Loans	41,636	57,860
Total Loans	6,547,538	5,737,017
Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	29,402	6,579	6,749
Residential mortgage loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	4,673,266	4,290,152
Accruing	19,664	17,406
Non-accrual Loans	34,833	30,396
Total Loans	4,739,075	4,359,156
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	40,219	37,440	$ 37,177
Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Current	1,942,091	2,258,659
Accruing	15,057	12,692
Non-accrual Loans	24,404	18,830
Total Loans	1,987,336	2,304,694
Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Current	675,014	721,231
Accruing	4,949	6,296
Non-accrual Loans	3,381	2,846
Total Loans	683,455	730,643
Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	265,328	363,413
Acquired Loans | Commercial Loans | Real estate - construction
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	8,567	26,423
Acquired Loans | Commercial Loans | Real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	55,533	72,652
Acquired Loans | Commercial Loans | Real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	52,257	69,255
Acquired Loans | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	22,581	26,841
Acquired Loans | Residential mortgage loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	75,811	93,208
Acquired Loans | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	48,385	72,655
Acquired Loans | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Acquired Impaired Loans	2,194	2,379
Current or Less Than 30 days past due
Accounts, Notes, Loans and Financing Receivable
Current	23,545,805	21,959,758
Current or Less Than 30 days past due | Commercial Loans | Real estate - construction
Accounts, Notes, Loans and Financing Receivable
Current	1,311,458	1,167,795
Current or Less Than 30 days past due | Commercial Loans | Real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	2,384,204	2,305,743
Current or Less Than 30 days past due | Commercial Loans | Real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Current	6,194,061	5,703,131
Current or Less Than 30 days past due | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Current	6,474,894	5,645,304
Current or Less Than 30 days past due | Residential mortgage loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Current	4,608,767	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	1,899,490	2,200,517
Current or Less Than 30 days past due | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Current	672,931	719,122
30-59 days
Accounts, Notes, Loans and Financing Receivable
Accruing	44,119	38,579
30-59 days | Commercial Loans | Real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	244	1,054
30-59 days | Commercial Loans | Real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	15,619	7,167
30-59 days | Commercial Loans | Real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,831	7,473
30-59 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	6,414	5,139
30-59 days | Residential mortgage loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	2,335	2,768
30-59 days | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	12,916	10,283
30-59 days | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Accruing	3,760	4,695
60-89 days
Accounts, Notes, Loans and Financing Receivable
Accruing	24,085	18,753
60-89 days | Commercial Loans | Real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
60-89 days | Commercial Loans | Real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	1,118	0
60-89 days | Commercial Loans | Real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	2,459	360
60-89 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	1,126	1,320
60-89 days | Residential mortgage loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	16,052	13,063
60-89 days | Consumer and Other Loans | Consumer - home equity
Accounts, Notes, Loans and Financing Receivable
Accruing	2,141	2,409
60-89 days | Consumer and Other Loans | Consumer - other
Accounts, Notes, Loans and Financing Receivable
Accruing	1,189	1,601
Greater than 90 days
Accounts, Notes, Loans and Financing Receivable
Accruing	3,257	2,128
Greater than 90 days | Commercial Loans | Real estate - construction
Accounts, Notes, Loans and Financing Receivable
Accruing	0	0
Greater than 90 days | Commercial Loans | Real estate - owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	1,035	0
Greater than 90 days | Commercial Loans | Real estate - non-owner-occupied
Accounts, Notes, Loans and Financing Receivable
Accruing	58	0
Greater than 90 days | Commercial Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Accruing	887	553
Greater than 90 days | Residential mortgage loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Accruing	1,277	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