Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Net income	$ 447,249	$ 268,822
Net Income (Loss)	447,249	268,822
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,486,993	1,506,165
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income	46,271	32,926
Net Income (Loss)	46,271	32,926
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	155,903	137,833
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	669	885
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income	122,638	143,732
Net Income (Loss)	122,638	143,732
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	285,912	291,776
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	809	1,053
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income	71,272	117,408
Net Income (Loss)	71,272	117,408
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	200,843	223,305
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	222	409
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income	90,546	25,668
Net Income (Loss)	90,546	25,668
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	134,544	49,219
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(10,027)	(13,037)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income	49,611	24,616
Net Income (Loss)	49,611	24,616
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	153,760	125,561
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	22,183	21,417
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income	85,358	110,246
Net Income (Loss)	85,358	110,246
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	346,917	402,683
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	272	267
All Other [Member]
Segment Reporting Information [Line Items]
Net income	(18,447)	(185,774)
Net Income (Loss)	(18,447)	(185,774)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	209,114	275,788
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (14,128)	$ (10,994)