Segment Information - Summary of Reclassified Segment Information on Comparable Basis (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net income	$ 352,610	$ 348,927
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,434,213	1,361,105
As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		348,927
As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		1,361,105
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income	37,718	24,988
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	127,884	120,333
Business Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		22,407
Business Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		115,981
Business Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		2,581
Business Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		4,352
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income	125,465	112,787
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	266,396	273,908
Commercial Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		112,750
Commercial Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		273,845
Commercial Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		37
Commercial Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		63
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income	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] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		84,547
Commercial Real Estate [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		195,125
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income	19,739	33,945
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	50,038	78,946
Discretionary Portfolio [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		33,945
Discretionary Portfolio [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		78,946
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income	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] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		14,844
Residential Mortgage Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		93,708
Residential Mortgage Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		(4,927)
Residential Mortgage Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		(8,307)
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income	123,380	86,191
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	393,476	368,518
Retail Banking [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		81,873
Retail Banking [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		361,237
Retail Banking [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		4,318
Retail Banking [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		7,281
All Other [Member]
Segment Reporting Information [Line Items]
Net income	(76,941)	(3,448)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ 311,354	238,874
All Other [Member] | As Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income		(1,439)
All Other [Member] | As Previously Reported [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		242,263
All Other [Member] | Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income		(2,009)
All Other [Member] | Impact of Changes [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues		$ (3,389)