Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 348,927	$ 298,528
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,361,105	1,292,897
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	22,407	25,448
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	115,981	113,689
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	911	991
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	112,750	101,327
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	273,845	253,617
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	920	1,056
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	84,547	80,529
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	195,125	177,380
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	407	387
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	33,945	48,410
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	78,946	101,036
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(12,927)	(14,323)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	14,844	17,077
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	93,708	96,935
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	18,211	19,660
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	81,873	63,288
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	361,237	339,046
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	3,047	3,014
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(1,439)	(37,551)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	242,263	211,194
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (10,569)	$ (10,785)