Allowance for Credit Losses - Loan and Leases Considered Nonaccrual and Interest Income Recognized on Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2020	Jan. 01, 2019	Jan. 01, 2018
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	$ 974,782	$ 399,274	$ 375,709
Amortized Cost without Allowance	918,517	563,838	517,899
Total	1,893,299	963,112	893,608
Amortized Cost				$ 1,134,333	$ 893,608	$ 882,598
Interest Income Recognized	54,217	36,807	46,838
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	226,897	206,644	126,753
Amortized Cost without Allowance	79,930	139,913	107,670
Total	306,827	346,557	234,423
Amortized Cost				346,743	234,423	240,991
Interest Income Recognized	11,269	8,960	7,873
Commercial [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	364,110	40,847	90,296
Amortized Cost without Allowance	411,784	117,627	113,376
Total	775,894	158,474	203,672
Amortized Cost				173,796	203,672	184,982
Interest Income Recognized	7,821	5,850	10,880
Residential Builder and Developer [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	1,094	604	2,205
Amortized Cost without Allowance		3,378	2,593
Total	1,094	3,982	4,798
Amortized Cost				4,708	4,798	6,451
Interest Income Recognized	1,694	357	1,779
Other Commercial Construction [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	20,992	12,425	14,604
Amortized Cost without Allowance	93,047	20,345	7,601
Total	114,039	32,770	22,205
Amortized Cost				35,881	22,205	10,088
Interest Income Recognized	8,457	634	3,474
Residential [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	159,006	59,982	57,346
Amortized Cost without Allowance	206,723	175,681	176,006
Total	365,729	235,663	233,352
Amortized Cost				322,504	233,352	235,834
Interest Income Recognized	18,069	12,630	14,065
Residential Limited Documentation [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	84,568	26,710	26,808
Amortized Cost without Allowance	62,602	56,717	57,877
Total	147,170	83,427	84,685
Amortized Cost				114,667	84,685	96,105
Interest Income Recognized	634	1,092	1,980
Home Equity Lines and Loans [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	61,031	24,812	30,819
Amortized Cost without Allowance	18,361	38,403	40,473
Total	79,392	63,215	71,292
Amortized Cost				65,039	71,292	74,500
Interest Income Recognized	4,092	5,987	5,535
Recreational Finance [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	19,434	9,054	6,016
Amortized Cost without Allowance	6,085	5,165	5,183
Total	25,519	14,219	11,199
Amortized Cost				14,308	11,199	6,509
Interest Income Recognized	626	575	333
Automobile [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	34,044	14,805	16,271
Amortized Cost without Allowance	5,360	6,488	7,088
Total	39,404	21,293	23,359
Amortized Cost				21,293	23,359	23,781
Interest Income Recognized	186	214	689
Other [Member]
Financing Receivable Impaired [Line Items]
Amortized Cost with Allowance	3,606	3,391	4,591
Amortized Cost without Allowance	34,625	121	32
Total	38,231	3,512	4,623
Amortized Cost				$ 35,394	$ 4,623	$ 3,357
Interest Income Recognized	$ 1,369	$ 508	$ 230