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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	$ 28,530	$ 6,456	$ 17,888	$ 16,249
Noninterest income	120,456	105,398	218,880	212,780
Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income	46,321	42,903	93,321	84,860
Trading And Investment Banking
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	12,828	5,319	13,895	10,772
Noninterest income	12,851	5,453	14,574	11,034
Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	49	34	92	69
Noninterest income	19,074	20,747	44,155	42,028
Insurance Fees and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income	533	465	792	803
Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Noninterest income	5,753	7,077	15,613	14,320
Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	(6,209)	(9,694)	(14,366)	(17,755)
Noninterest income	12,916	16,439	29,461	33,506
Gains Losses On Sales Of Securities Available For Sale, Net [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	4,006	(1,403)	5,233	(594)
Noninterest income	4,006	(1,403)	5,233	(594)
Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue (Expense) out of Scope of ASC 606	17,856	12,200	13,034	23,757
Noninterest income	19,002	13,717	15,731	26,823
Commercial Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	18,023	22,952	40,362	45,288
Noninterest income	24,078	20,387	35,318	43,568
Commercial Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	6,891	7,392	13,783	14,853
Commercial Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	58	55	117	103
Commercial Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	10,913	15,213	25,901	29,701
Commercial Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	161	292	561	631
Institutional Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	49,567	48,698	109,844	97,878
Noninterest income	66,488	55,626	128,440	111,476
Institutional Banking [Member] | Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	31,355	27,251	62,617	53,940
Institutional Banking [Member] | Trading And Investment Banking
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	23	134	679	262
Institutional Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	10,462	10,632	26,069	21,709
Institutional Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	3,822	5,026	11,412	10,448
Institutional Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	3,535	5,274	8,259	10,799
Institutional Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	370	381	808	720
Personal Banking [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	24,336	27,292	50,786	53,365
Noninterest income	29,890	29,385	55,122	57,736
Personal Banking [Member] | Trust and Securities Processing [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	14,966	15,652	30,704	30,920
Personal Banking [Member] | Service Charges On Deposit Accounts [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	1,672	2,689	4,211	5,397
Personal Banking [Member] | Insurance Fees and Commissions [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	533	465	792	803
Personal Banking [Member] | Brokerage Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	1,873	1,996	4,084	3,769
Personal Banking [Member] | Bankcard Fees [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	4,677	5,646	9,667	10,761
Personal Banking [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Revenue Scope of ASC 606	$ 615	$ 844	$ 1,328	$ 1,715