Loans and Allowance for Credit Losses - Rollforward of Allowance for Credit/Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 191,146			$ 101,788
Charge-offs	(6,358)			(16,122)
Recoveries	817			2,909
Provision	18,000			106,000
Ending balance - ACL	203,605			203,605
Beginning balance - ACL on off-balance sheet	2,978			2,978
Provision	3,500			3,500
Ending balance - ACL on off-balance sheet	6,478			6,478
Beginning balance			$ 103,661	101,788	[1]	$ 103,635
Charge-offs			(14,443)			(28,187)
Recoveries			1,874			3,294
Provision			11,000			23,350
Ending balance	200,300	[1]	102,092	200,300	[1]	102,092
Ending balance: individually evaluated for impairment			2,751			2,751
Ending balance: collectively evaluated for impairment			99,341			99,341
Ending balance: loans	15,305,097		12,900,269	15,305,097		12,900,269
Ending balance: individually evaluated for impairment			48,818			48,818
Ending balance: collectively evaluated for impairment			12,851,451			12,851,451
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	122,532			63,313
Charge-offs	(1,121)			(2,436)
Recoveries	241			1,717
Provision	(7,042)			48,339
Ending balance - ACL	114,610			114,610
Beginning balance - ACL on off-balance sheet	2,263			2,263
Provision	3,154			3,154
Ending balance - ACL on off-balance sheet	5,417			5,417
Commercial and Industrial Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				3,677
Specialty Lending Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,549			2,545
Provision	(2,620)			(1,764)
Ending balance - ACL	929			929
Beginning balance - ACL on off-balance sheet	53			53
Provision	28			28
Ending balance - ACL on off-balance sheet	81			81
Specialty Lending Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				148
Commercial Real Estate Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	35,395			15,951
Charge-offs	(2,858)			(8,920)
Recoveries	55			76
Provision	23,242			47,801
Ending balance - ACL	55,834			55,834
Beginning balance - ACL on off-balance sheet	257			257
Provision	146			146
Ending balance - ACL on off-balance sheet	403			403
Commercial Real Estate Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				926
Consumer Real Estate Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	4,177			2,623
Charge-offs	(206)			(219)
Recoveries	34			48
Provision	1,947			3,348
Ending balance - ACL	5,952			5,952
Beginning balance - ACL on off-balance sheet	102			102
Provision	212			212
Ending balance - ACL on off-balance sheet	314			314
Consumer Real Estate Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				152
Consumer Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,127			543
Charge-offs	(158)			(406)
Recoveries	118			215
Provision	519			1,223
Ending balance - ACL	1,606			1,606
Beginning balance - ACL on off-balance sheet	22			22
Provision	11			11
Ending balance - ACL on off-balance sheet	33			33
Beginning balance			8,928			9,071
Charge-offs			(2,122)			(4,589)
Recoveries			629			1,350
Provision			1,382			2,985
Ending balance			8,817			8,817
Ending balance: collectively evaluated for impairment			8,817			8,817
Ending balance: loans			355,736			355,736
Ending balance: collectively evaluated for impairment			355,736			355,736
Consumer Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				31
Credit Cards Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	18,823			15,739
Charge-offs	(2,004)			(4,130)
Recoveries	369			853
Provision	2,397			6,209
Ending balance - ACL	19,585			19,585
Credit Cards Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				914
Leases and Other Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,308			1,074
Charge-offs	(11)			(11)
Provision	(513)			659
Ending balance - ACL	1,784			1,784
Beginning balance - ACL on off-balance sheet	211			211
Provision	(38)			(38)
Ending balance - ACL on off-balance sheet	173			173
Leases and Other Portfolio [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				62
Total - Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	187,911			101,788
Charge-offs	(6,358)			(16,122)
Recoveries	817			2,909
Provision	17,930			105,815
Ending balance - ACL	200,300			200,300
Beginning balance - ACL on off-balance sheet	2,908			2,908
Provision	3,513			3,513
Ending balance - ACL on off-balance sheet	6,421			6,421
Total - Loans [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				5,910
HTM [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,235
Provision	70			185
Ending balance - ACL	3,305			3,305
Beginning balance - ACL on off-balance sheet	70			70
Provision	(13)			(13)
Ending balance - ACL on off-balance sheet	$ 57			57
HTM [Member] | ASU 2016-13 Adjustment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
ASU 2016-13 adjustment				$ 3,120
Commercial Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance			80,332			80,888
Charge-offs			(12,170)			(23,333)
Recoveries			380			1,006
Provision			7,466			17,447
Ending balance			76,008			76,008
Ending balance: individually evaluated for impairment			2,672			2,672
Ending balance: collectively evaluated for impairment			73,336			73,336
Ending balance: loans			6,356,633			6,356,633
Ending balance: individually evaluated for impairment			28,143			28,143
Ending balance: collectively evaluated for impairment			6,328,490			6,328,490
Real Estate Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance			14,390			13,664
Charge-offs			(151)			(265)
Recoveries			865			938
Provision			2,153			2,920
Ending balance			17,257			17,257
Ending balance: individually evaluated for impairment			79			79
Ending balance: collectively evaluated for impairment			17,178			17,178
Ending balance: loans			6,183,167			6,183,167
Ending balance: individually evaluated for impairment			20,675			20,675
Ending balance: collectively evaluated for impairment			6,162,492			6,162,492
Leases Portfolio [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance			11			12
Provision			(1)			(2)
Ending balance			10			10
Ending balance: collectively evaluated for impairment			10			10
Ending balance: loans			4,733			4,733
Ending balance: collectively evaluated for impairment			$ 4,733			$ 4,733

[1] As of December 31, 2019, this line represents the Allowance for loan losses. See further discussion of this change in Note 3, “New Accounting Pronouncements.”