Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 352,610	$ 348,927
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,434,213	1,361,105
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	37,718	24,988
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	127,884	120,333
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	918	911
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	125,465	112,787
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	266,396	273,908
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	850	920
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	108,303	84,547
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	202,607	195,125
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	340	407
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	19,739	33,945
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	50,038	78,946
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(10,832)	(12,927)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	14,946	9,917
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	82,458	85,401
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	15,421	18,211
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	123,380	86,191
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	393,476	368,518
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,865	3,047
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(76,941)	(3,448)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	311,354	238,874
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (9,562)	$ (10,569)