Loans and Allowance for Credit Losses - Rollforward of Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 101,788
Adjusted beginning balance	110,818
Charge-offs	(28,689)
Recoveries	8,564
Provision	127,890
Ending balance - ACL	218,583		$ 101,788
Beginning balance - ACL on off-balance sheet	2,978
Provision	2,610
Ending balance - ACL on off-balance sheet	5,588		2,978
Beginning balance	101,788	[1]	103,635		$ 100,604
Charge-offs			(46,080)		(77,543)
Recoveries			11,383		9,824
Provision			32,850		70,750
Ending Balance	215,973	[1]	101,788	[1]	103,635
Ending Balance: individually evaluated for impairment			738		4,711
Ending Balance: collectively evaluated for impairment			101,050		98,924
Ending Balance: loans	16,103,651		13,431,722		12,178,150
Ending Balance: individually evaluated for impairment			51,816		39,239
Ending Balance: collectively evaluated for impairment			13,379,906		12,138,911
ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	9,030
Commercial and Industrial Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	63,313
Adjusted beginning balance	66,990
Charge-offs	(8,587)
Recoveries	6,473
Provision	57,824
Ending balance - ACL	122,700		63,313
Beginning balance - ACL on off-balance sheet	2,263
Provision	1,596
Ending balance - ACL on off-balance sheet	3,859		2,263
Commercial and Industrial Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	3,677
Credit Cards Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	15,739
Adjusted beginning balance	16,653
Charge-offs	(7,326)
Recoveries	1,618
Provision	4,841
Ending balance - ACL	15,786		15,739
Credit Cards Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	914
Specialty Lending Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,545
Adjusted beginning balance	2,693
Provision	2,526
Ending balance - ACL	5,219		2,545
Beginning balance - ACL on off-balance sheet	53
Provision	234
Ending balance - ACL on off-balance sheet	287		53
Specialty Lending Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	148
Leases and Other Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,074
Adjusted beginning balance	1,136
Charge-offs	(11)
Recoveries	6
Provision	1,140
Ending balance - ACL	2,271		1,074
Beginning balance - ACL on off-balance sheet	211
Provision	203
Ending balance - ACL on off-balance sheet	414		211
Leases and Other Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	62
Commercial Real Estate Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	15,951
Adjusted beginning balance	16,877
Charge-offs	(11,939)
Recoveries	91
Provision	56,902
Ending balance - ACL	61,931		15,951
Beginning balance - ACL on off-balance sheet	257
Provision	190
Ending balance - ACL on off-balance sheet	447		257
Commercial Real Estate Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	926
Total - Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	101,788
Adjusted beginning balance	107,698
Charge-offs	(28,689)
Recoveries	8,564
Provision	128,400
Ending balance - ACL	215,973		101,788
Beginning balance - ACL on off-balance sheet	2,908
Provision	2,625
Ending balance - ACL on off-balance sheet	5,533		2,908
Total - Loans [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	5,910
Consumer Real Estate Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,623
Adjusted beginning balance	2,775
Charge-offs	(219)
Recoveries	69
Provision	3,961
Ending balance - ACL	6,586		2,623
Beginning balance - ACL on off-balance sheet	102
Provision	43
Ending balance - ACL on off-balance sheet	145		102
Consumer Real Estate Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	152
HTM [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Adjusted beginning balance	3,120
Provision	(510)
Ending balance - ACL	2,610
Beginning balance - ACL on off-balance sheet	70
Provision	(15)
Ending balance - ACL on off-balance sheet	55		70
HTM [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	3,120
Consumer Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	543
Adjusted beginning balance	574
Charge-offs	(607)
Recoveries	307
Provision	1,206
Ending balance - ACL	1,480		543
Beginning balance - ACL on off-balance sheet	22
Provision	359
Ending balance - ACL on off-balance sheet	381		22
Beginning balance	10,211		9,071		10,083
Charge-offs			(8,920)		(9,744)
Recoveries			2,515		2,626
Provision			7,545		6,106
Ending Balance			10,211		9,071
Ending Balance: collectively evaluated for impairment			10,211		9,071
Ending Balance: loans			360,216		375,767
Ending Balance: collectively evaluated for impairment			360,216		375,767
Consumer Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment	31
Commercial Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	71,258		80,888		81,156
Charge-offs			(36,716)		(64,371)
Recoveries			7,746		6,753
Provision			19,340		57,350
Ending Balance			71,258		80,888
Ending Balance: individually evaluated for impairment			271		4,605
Ending Balance: collectively evaluated for impairment			70,987		76,283
Ending Balance: loans			6,487,031		6,037,065
Ending Balance: individually evaluated for impairment			25,769		31,006
Ending Balance: collectively evaluated for impairment			6,461,262		6,006,059
Real Estate Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	20,314		13,664		9,312
Charge-offs			(444)		(3,428)
Recoveries			1,122		445
Provision			5,972		7,335
Ending Balance			20,314		13,664
Ending Balance: individually evaluated for impairment			467		106
Ending Balance: collectively evaluated for impairment			19,847		13,558
Ending Balance: loans			6,582,497		5,760,070
Ending Balance: individually evaluated for impairment			26,047		8,233
Ending Balance: collectively evaluated for impairment			6,556,450		5,751,837
Leases Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 5		12		53
Provision			(7)		(41)
Ending Balance			5		12
Ending Balance: collectively evaluated for impairment			5		12
Ending Balance: loans			1,978		5,248
Ending Balance: collectively evaluated for impairment			$ 1,978		$ 5,248

[1] As of December 31, 2019, this line represents the Allowance for loan losses. See further discussion of this change in Note 2, “New Accounting Pronouncements”