Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 482,742	$ 352,610
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,550,825	1,434,213
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	43,271	37,718
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	139,322	127,884
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	856	918
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	132,218	125,465
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	267,490	266,396
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	840	850
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	117,498	108,303
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	219,173	202,607
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	354	340
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	39,172	19,739
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	63,917	50,038
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(9,299)	(10,832)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	12,941	14,946
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	83,761	82,458
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	14,514	15,421
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	145,066	123,380
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	430,891	393,476
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,511	2,865
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(7,424)	(76,941)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	346,271	311,354
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (9,776)	$ (9,562)