Business Segments - Schedule of Financial Data for Business Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Average interest earning assets	$ 15,040,783				$ 14,242,202				$ 15,040,783	$ 14,242,202	$ 14,109,728
Interest income	170,942	155,459	157,164	153,038	156,915	153,779	152,370	153,033	636,603	616,097	671,193
Interest expense	42,296	40,791	39,745	39,014	40,787	42,110	42,483	42,997	161,846	168,377	181,312
Net Interest Income	128,646	114,668	117,419	114,024	116,128	111,669	109,887	110,036	474,757	447,720	489,881
Provision for credit losses	3,980	(423)	(5,671)	3,998	6,440	5,334	2,552	1,769	1,884	16,095	25,552
Net Interest Income After Provision for Credit Losses									472,873	431,625	464,329
Non-interest income									77,616	128,653	120,946
Non-interest expense:					88,178	92,434	92,718	93,656	403,255	381,338	374,900
Internal expense transfer									0	0	0
Income before income taxes	32,962	38,336	41,271	34,665	55,669	34,264	44,883	44,124	147,234	178,940	210,375
Return on average interest earning assets (pre-tax)	0.98%				1.26%				0.98%	1.26%	1.49%
Consumer Lending
Segment Reporting Information [Line Items]
Average interest earning assets	4,122,468				3,915,395				4,122,468	3,915,395	3,941,374
Interest income									154,078	157,482	174,978
Interest expense									41,343	41,556	45,499
Net Interest Income									112,735	115,926	129,479
Provision for credit losses									438	2,094	4,969
Net Interest Income After Provision for Credit Losses									112,297	113,832	124,510
Non-interest income									40,611	75,028	83,765
Non-interest expense:									59,051	77,231	69,281
Internal expense transfer									65,477	64,142	65,561
Income before income taxes									28,380	47,487	73,433
Return on average interest earning assets (pre-tax)	0.69%				1.21%				0.69%	1.21%	1.86%
Commercial Lending
Segment Reporting Information [Line Items]
Average interest earning assets	7,959,215				7,272,573				7,959,215	7,272,573	7,296,895
Interest income									399,192	380,369	407,288
Interest expense									79,820	77,187	84,234
Net Interest Income									319,372	303,182	323,054
Provision for credit losses									1,446	14,001	20,583
Net Interest Income After Provision for Credit Losses									317,926	289,181	302,471
Non-interest income									(19,624)	(7,219)	(1,701)
Non-interest expense:									58,142	57,096	54,963
Internal expense transfer									126,465	118,546	120,993
Income before income taxes									113,695	106,320	124,814
Return on average interest earning assets (pre-tax)	1.43%				1.46%				1.43%	1.46%	1.71%
Investment Management
Segment Reporting Information [Line Items]
Average interest earning assets	2,959,100				3,054,234				2,959,100	3,054,234	2,871,459
Interest income									91,689	86,564	96,582
Interest expense									29,676	32,416	33,148
Net Interest Income									62,013	54,148	63,434
Provision for credit losses									0	0	0
Net Interest Income After Provision for Credit Losses									62,013	54,148	63,434
Non-interest income									6,392	5,962	6,817
Non-interest expense:									1,369	1,355	1,219
Internal expense transfer									47,060	50,011	47,749
Income before income taxes									19,976	8,744	21,283
Return on average interest earning assets (pre-tax)	0.68%				0.29%				0.68%	0.29%	0.74%
Corporate and Other Adjustments
Segment Reporting Information [Line Items]
Average interest earning assets	0				0				0	0	0
Interest income									(8,356)	(8,318)	(7,655)
Interest expense									11,007	17,218	18,431
Net Interest Income									(19,363)	(25,536)	(26,086)
Provision for credit losses									0	0	0
Net Interest Income After Provision for Credit Losses									(19,363)	(25,536)	(26,086)
Non-interest income									50,237	54,882	32,065
Non-interest expense:									284,693	245,656	249,437
Internal expense transfer									(239,002)	(232,699)	(234,303)
Income before income taxes									$ (14,817)	$ 16,389	$ (9,155)