Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Net income (loss)	$ 298,528	$ 241,613
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	25,448	24,811
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	101,327	96,423
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)	80,529	82,591
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)	39,988	5,954
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	17,077	29,460
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	63,288	68,888
All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)	(29,129)	(66,514)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,292,897	1,099,791
Operating Segments [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	113,689	108,560
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	253,617	246,581
Operating Segments [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Total revenues	177,380	169,021
Operating Segments [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Total revenues	86,835	15,474
Operating Segments [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	96,935	105,757
Operating Segments [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	339,046	300,391
Operating Segments [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Total revenues	225,395	154,007
Intersegment Activity Eliminated in Consolidated Totals [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	991	1,045
Intersegment Activity Eliminated in Consolidated Totals [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	1,056	1,085
Intersegment Activity Eliminated in Consolidated Totals [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Total revenues	387	82
Intersegment Activity Eliminated in Consolidated Totals [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Total revenues	(14,323)	(5,443)
Intersegment Activity Eliminated in Consolidated Totals [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	19,660	11,387
Intersegment Activity Eliminated in Consolidated Totals [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	3,014	3,137
Intersegment Activity Eliminated in Consolidated Totals [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (10,785)	$ (11,293)