Business Segments - Schedule of Financial Data for Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 17,425,504				$ 15,040,783				$ 17,425,504	$ 15,040,783	$ 14,242,202
Interest income	185,594	$ 174,690	$ 175,754	$ 170,985	170,942	$ 155,459	$ 157,164	$ 153,038	707,023	636,603	616,097
Interest expense	37,548	40,730	39,577	38,899	42,296	40,791	39,745	39,014	156,754	161,846	168,377
Net Interest Income	148,046	133,960	136,177	132,086	128,646	114,668	117,419	114,024	550,269	474,757	447,720
Provision for credit losses	3,507	94	4,500	0	3,980	(423)	(5,671)	3,998	8,101	1,884	16,095
Net Interest Income After Provision for Credit Losses									542,168	472,873	431,625
Non-interest income									83,802	77,616	128,653
Non-interest expense:									499,075	403,255	381,338
Internal expense transfer									0	0	0
Income (loss) before income taxes	$ (6,316)	$ 46,133	$ 44,465	$ 42,613	$ 32,962	$ 38,336	$ 41,271	$ 34,665	$ 126,895	$ 147,234	$ 178,940
Return on average interest earning assets (pre-tax)	0.73%				0.98%				0.73%	0.98%	1.26%
Corporate and Other Adjustments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 0				$ 0				$ 0	$ 0	$ 0
Interest income									(8,277)	(8,356)	(8,318)
Interest expense									11,233	11,007	17,218
Net Interest Income									(19,510)	(19,363)	(25,536)
Provision for credit losses									0	0	0
Net Interest Income After Provision for Credit Losses									(19,510)	(19,363)	(25,536)
Non-interest income									30,937	50,237	54,882
Non-interest expense:									370,051	284,693	245,656
Internal expense transfer									(264,364)	(239,002)	(232,699)
Income (loss) before income taxes									(94,260)	(14,817)	16,389
Consumer Lending | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 4,764,306				$ 4,122,468				4,764,306	4,122,468	3,915,395
Interest income									170,569	154,078	157,482
Interest expense									39,787	41,343	41,556
Net Interest Income									130,782	112,735	115,926
Provision for credit losses									1,153	438	2,094
Net Interest Income After Provision for Credit Losses									129,629	112,297	113,832
Non-interest income									45,306	40,611	75,028
Non-interest expense:									59,794	59,051	77,231
Internal expense transfer									72,441	65,477	64,142
Income (loss) before income taxes									$ 42,700	$ 28,380	$ 47,487
Return on average interest earning assets (pre-tax)	0.90%				0.69%				0.90%	0.69%	1.21%
Commercial Lending | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 9,682,714				$ 7,959,215				$ 9,682,714	$ 7,959,215	$ 7,272,573
Interest income									463,062	399,192	380,369
Interest expense									80,861	79,820	77,187
Net Interest Income									382,201	319,372	303,182
Provision for credit losses									6,948	1,446	14,001
Net Interest Income After Provision for Credit Losses									375,253	317,926	289,181
Non-interest income									744	(19,624)	(7,219)
Non-interest expense:									68,156	58,142	57,096
Internal expense transfer									146,463	126,465	118,546
Income (loss) before income taxes									$ 161,378	$ 113,695	$ 106,320
Return on average interest earning assets (pre-tax)	1.67%				1.43%				1.67%	1.43%	1.46%
Investment Management | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 2,978,484				$ 2,959,100				$ 2,978,484	$ 2,959,100	$ 3,054,234
Interest income									81,669	91,689	86,564
Interest expense									24,873	29,676	32,416
Net Interest Income									56,796	62,013	54,148
Provision for credit losses									0	0	0
Net Interest Income After Provision for Credit Losses									56,796	62,013	54,148
Non-interest income									6,815	6,392	5,962
Non-interest expense:									1,074	1,369	1,355
Internal expense transfer									45,460	47,060	50,011
Income (loss) before income taxes									$ 17,077	$ 19,976	$ 8,744
Return on average interest earning assets (pre-tax)	0.57%				0.68%				0.57%	0.68%	0.29%