Revenue Recognition - Summary of Disaggregation of Revenue According to Revenue Stream and Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606									$ 160,562	$ 24,091	$ 7,572
Noninterest income	$ 228,290	$ 112,996	$ 120,456	$ 98,424	$ 110,355	$ 103,635	$ 105,398	$ 107,382	560,166	426,770	401,698
Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income									194,646	176,913	172,163
Trading and Investment Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606									32,190	22,725	15,584
Noninterest income									32,945	23,466	15,584
Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606									211	145	126
Noninterest income									83,879	82,748	84,287
Insurance Fees and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income									1,369	1,634	1,292
Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income									24,350	31,261	25,807
Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606									(29,065)	(36,945)	(35,236)
Noninterest income									60,544	66,727	68,520
Investment Securities Gains, Net [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606									120,634	2,245	3,521
Noninterest income									120,634	2,245	3,521
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606									36,592	35,921	23,577
Noninterest income									41,799	41,776	30,524
Commercial Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									81,871	91,501	92,185
Noninterest income									189,412	81,609	74,931
Commercial Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									28,736	29,716	30,313
Commercial Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									245	214	194
Commercial Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									51,755	60,375	59,596
Commercial Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									1,135	1,196	2,082
Institutional Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									213,890	202,063	189,986
Noninterest income									254,874	232,444	208,423
Institutional Banking [Member] | Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									131,249	113,313	107,237
Institutional Banking [Member] | Trading and Investment Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									755	741
Institutional Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									46,611	41,923	42,297
Institutional Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									16,075	23,231	17,026
Institutional Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									17,731	21,386	22,080
Institutional Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									1,469	1,469	1,346
Personal Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									103,843	109,115	111,955
Noninterest income									115,880	112,717	118,344
Personal Banking [Member] | Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									63,397	63,600	64,926
Personal Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									8,321	10,964	11,551
Personal Banking [Member] | Insurance Fees and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									1,369	1,634	1,292
Personal Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									8,030	7,816	8,587
Personal Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									20,123	21,911	22,080
Personal Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606									$ 2,603	$ 3,190	$ 3,519