Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net interest income	$ 3,824,778	$ 3,866,317	$ 4,130,264
Noninterest income	2,166,994	2,088,444	2,061,679
Total income	5,991,772	5,954,761	6,191,943
Provision for credit losses	(75,000)	800,000	176,000
Amortization of core deposit and other intangible assets	10,167	14,869	19,490
Depreciation and other amortization	314,041	305,419	281,825
Other noninterest expense	3,287,415	3,064,952	3,167,367
Income before taxes	2,455,149	1,769,521	2,547,261
Income tax expense (benefit)	596,403	416,369	618,112
Net income	1,858,746	1,353,152	1,929,149
Average total assets	152,669,000	135,480,000	119,584,000
Capital expenditures	149,000	172,000	178,000
All Other [Member]
Segment Reporting Information [Line Items]
Net interest income	105,876	121,808	537,940
Noninterest income	746,240	725,472	695,443
Total income	852,116	847,280	1,233,383
Provision for credit losses	(313,145)	482,202	6,257
Amortization of core deposit and other intangible assets	9,107	13,809	18,430
Depreciation and other amortization	123,881	116,979	108,604
Other noninterest expense	1,082,993	959,258	1,117,668
Income before taxes	(50,720)	(724,968)	(17,576)
Income tax expense (benefit)	(26,741)	(202,396)	(28,625)
Net income	(23,979)	(522,572)	11,049
Average total assets	43,853,000	22,996,000	14,953,000
Capital expenditures	93,000	138,000	98,000
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	518,940	462,614	451,307
Noninterest income	123,854	103,837	113,855
Total income	642,794	566,451	565,162
Provision for credit losses	10,928	25,928	16,501
Depreciation and other amortization	1,106	1,482	2,066
Other noninterest expense	341,751	322,868	317,482
Income before taxes	289,009	216,173	229,113
Income tax expense (benefit)	75,545	56,953	60,617
Net income	213,464	159,220	168,496
Average total assets	8,007,000	8,152,000	5,793,000
Capital expenditures	1,000		1,000
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	854,264	864,149	828,888
Noninterest income	302,974	276,791	289,558
Total income	1,157,238	1,140,940	1,118,446
Provision for credit losses	101,060	73,099	25,580
Depreciation and other amortization	2,362	2,421	2,353
Other noninterest expense	384,505	375,769	382,214
Income before taxes	669,311	689,651	708,299
Income tax expense (benefit)	175,588	181,179	187,835
Net income	493,723	508,472	520,464
Average total assets	28,559,000	30,338,000	28,142,000
Capital expenditures	1,000		2,000
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	643,415	673,894	692,526
Noninterest income	218,189	208,367	214,970
Total income	861,604	882,261	907,496
Provision for credit losses	67,405	107,210	1,537
Amortization of core deposit and other intangible assets	1,060	1,060	1,060
Depreciation and other amortization	35,623	28,187	26,963
Other noninterest expense	276,791	256,428	239,333
Income before taxes	480,725	489,376	638,603
Income tax expense (benefit)	108,399	107,548	152,977
Net income	372,326	381,828	485,626
Average total assets	25,628,000	25,792,000	23,921,000
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	483,624	486,831	209,807
Noninterest income	(38,638)	(1,735)	26,919
Total income	444,986	485,096	236,726
Provision for credit losses	3,622	1,508	3,608
Depreciation and other amortization	194	285	279
Other noninterest expense	64,122	54,339	52,885
Income before taxes	377,048	428,964	179,954
Income tax expense (benefit)	88,282	101,673	36,342
Net income	288,766	327,291	143,612
Average total assets	22,262,000	27,726,000	29,081,000
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	92,706	52,712	20,008
Noninterest income	523,765	515,549	393,372
Total income	616,471	568,261	413,380
Provision for credit losses	(562)	1,785	382
Depreciation and other amortization	57,716	60,129	48,248
Other noninterest expense	332,491	332,028	273,067
Income before taxes	226,826	174,319	91,683
Income tax expense (benefit)	53,866	40,667	19,355
Net income	172,960	133,652	72,328
Average total assets	6,463,000	4,038,000	2,611,000
Capital expenditures	1,000		1,000
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net interest income	1,125,953	1,204,309	1,389,788
Noninterest income	290,610	260,163	327,562
Total income	1,416,563	1,464,472	1,717,350
Provision for credit losses	55,692	108,268	122,135
Depreciation and other amortization	93,159	95,936	93,312
Other noninterest expense	804,762	764,262	784,718
Income before taxes	462,950	496,006	717,185
Income tax expense (benefit)	121,464	130,745	189,611
Net income	341,486	365,261	527,574
Average total assets	17,897,000	16,438,000	15,083,000
Capital expenditures	$ 53,000	$ 34,000	$ 76,000