Revenue Recognition - Summary of Disaggregation of Revenue According to Revenue Stream and Business Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	$ 25,929	$ 28,530	$ 30,438	$ 17,888
Noninterest income	131,589	120,456	240,486	218,880
Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income	53,863	46,321	108,697	93,321
Trading and Investment Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	8,350	12,828	17,405	13,895
Noninterest income	8,670	12,851	18,026	14,574
Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	78	49	148	92
Noninterest income	22,592	19,074	44,568	44,155
Insurance Fees and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income	245	533	665	792
Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income	2,592	5,753	5,926	15,613
Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	(8,810)	(6,209)	(16,426)	(14,366)
Noninterest income	16,063	12,916	30,736	29,461
Investment Securities Gains, Net [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	15,455	4,579	7,119	8,099
Noninterest income	15,455	4,579	7,119	8,099
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	10,856	17,283	22,192	10,168
Noninterest income	12,109	18,429	24,749	12,865
Commercial Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	22,763	18,023	42,956	40,362
Noninterest income	36,391	24,078	43,777	35,318
Commercial Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	8,230	6,891	15,758	13,783
Commercial Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	10	58	74	117
Commercial Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	14,327	10,913	26,697	25,901
Commercial Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	196	161	427	561
Institutional Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	58,725	49,567	115,623	109,844
Noninterest income	68,745	66,488	137,166	128,440
Institutional Banking [Member] | Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	40,118	31,355	77,603	62,617
Institutional Banking [Member] | Trading and Investment Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	320	23	621	679
Institutional Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	12,432	10,462	25,009	26,069
Institutional Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	673	3,822	1,992	11,412
Institutional Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	4,771	3,535	9,583	8,259
Institutional Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	411	370	815	808
Personal Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	24,172	24,336	51,469	50,786
Noninterest income	26,453	29,890	59,543	55,122
Personal Banking [Member] | Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	13,745	14,966	31,094	30,704
Personal Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	1,852	1,672	3,653	4,211
Personal Banking [Member] | Insurance Fees and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	245	533	665	792
Personal Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	1,909	1,873	3,860	4,084
Personal Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	5,775	4,677	10,882	9,667
Personal Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	$ 646	$ 615	$ 1,315	$ 1,328