Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net income	$ 458,069	$ 241,054	$ 905,318	$ 509,876
Average Total Assets	149,406,000	128,513,000	149,406,000	128,513,000	$ 135,480,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,455,973	1,444,410	2,942,966	2,950,575
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income	41,607	37,563	87,878	70,489
Average Total Assets	8,681,000	7,235,000	8,681,000	7,235,000	8,152,000
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	145,098	138,086	301,001	275,919
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	794	144	1,463	1,029
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income	111,035	111,030	233,673	254,762
Average Total Assets	29,927,000	30,603,000	29,927,000	30,603,000	30,338,000
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	284,659	287,525	570,571	579,301
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,012	249	1,821	1,302
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income	86,690	107,083	157,962	224,491
Average Total Assets	25,999,000	25,340,000	25,999,000	25,340,000	25,792,000
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	200,559	227,113	401,402	450,418
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	230	60	452	469
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income	78,532	95,691	169,078	121,359
Average Total Assets	22,769,000	26,821,000	22,769,000	26,821,000	27,726,000
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	118,307	138,827	252,851	188,046
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(10,079)	(9,861)	(20,106)	(22,898)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income	30,103	37,400	79,714	62,016
Average Total Assets	6,638,000	3,113,000	6,638,000	3,113,000	4,038,000
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	146,682	142,045	300,442	267,606
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	22,875	21,016	45,058	42,433
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income	89,200	86,498	174,558	196,744
Average Total Assets	17,444,000	16,039,000	17,444,000	16,039,000	16,438,000
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	350,988	353,521	697,905	756,204
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	281	267	553	534
All Other [Member]
Segment Reporting Information [Line Items]
Net income	20,902	(234,211)	2,455	(419,985)
Average Total Assets	37,948,000	19,362,000	37,948,000	19,362,000	$ 22,996,000
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	209,680	157,293	418,794	433,081
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (15,113)	$ (11,875)	$ (29,241)	$ (22,869)