Business Segments - Schedule of Financial Data for Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Average interest earning assets	$ 37,767,710	$ 30,494,569	$ 36,743,806	$ 29,981,699
Interest income	337,343	329,261	1,049,661	977,227
Interest expense	54,257	108,636	218,677	317,720
Net Interest Income	283,086	220,625	830,984	659,507
Provision for credit losses	30,908	8,700	106,747	18,800
Net Interest Income After Provision for Credit Losses	252,178	211,925	724,237	640,707
Non-interest income	49,272	41,150	135,499	176,426
Non-interest expense	160,185	145,877	473,007	435,409
Internal expense transfer	0	0	0	0
Income Before Income Taxes	$ 141,265	$ 107,198	$ 386,729	$ 381,724
Return on average interest earning assets (pre-tax)	1.50%	1.41%	1.40%	1.70%
Consumer Lending
Segment Reporting Information [Line Items]
Average interest earning assets	$ 7,126,157	$ 6,858,216	$ 7,187,839	$ 6,812,001
Interest income	63,956	68,253	199,018	203,897
Interest expense	9,048	23,552	40,217	69,504
Net Interest Income	54,908	44,701	158,801	134,393
Provision for credit losses	5,383	2,003	15,274	4,986
Net Interest Income After Provision for Credit Losses	49,525	42,698	143,527	129,407
Non-interest income	23,531	15,108	55,383	41,927
Non-interest expense	19,877	19,748	60,188	56,845
Internal expense transfer	18,614	19,758	58,355	58,476
Income Before Income Taxes	$ 34,565	$ 18,300	$ 80,367	$ 56,013
Return on average interest earning assets (pre-tax)	1.94%	1.07%	1.49%	1.10%
Commercial Lending
Segment Reporting Information [Line Items]
Average interest earning assets	$ 25,389,107	$ 19,278,529	$ 24,334,429	$ 18,839,194
Interest income	251,920	230,183	771,947	679,833
Interest expense	33,330	66,209	136,156	192,221
Net Interest Income	218,590	163,974	635,791	487,612
Provision for credit losses	25,637	6,697	90,785	13,814
Net Interest Income After Provision for Credit Losses	192,953	157,277	545,006	473,798
Non-interest income	20,421	15,057	52,192	29,527
Non-interest expense	25,633	25,161	73,041	76,729
Internal expense transfer	66,390	55,544	197,444	161,803
Income Before Income Taxes	$ 121,351	$ 91,629	$ 326,713	$ 264,793
Return on average interest earning assets (pre-tax)	1.91%	1.90%	1.79%	1.87%
Investment Management
Segment Reporting Information [Line Items]
Average interest earning assets	$ 5,252,446	$ 4,357,824	$ 5,221,538	$ 4,330,504
Interest income	22,513	31,999	81,905	97,189
Interest expense	6,728	14,965	29,216	44,185
Net Interest Income	15,785	17,034	52,689	53,004
Provision for credit losses	(112)	0	688	0
Net Interest Income After Provision for Credit Losses	15,897	17,034	52,001	53,004
Non-interest income	(1,304)	2,687	7,661	7,365
Non-interest expense	(186)	381	843	684
Internal expense transfer	13,713	12,559	42,393	37,245
Income Before Income Taxes	$ 1,066	$ 6,781	$ 16,426	$ 22,440
Return on average interest earning assets (pre-tax)	0.08%	0.62%	0.42%	0.69%
Corporate and Other Adjustments
Segment Reporting Information [Line Items]
Average interest earning assets	$ 0	$ 0	$ 0	$ 0
Interest income	(1,046)	(1,174)	(3,209)	(3,692)
Interest expense	5,151	3,910	13,088	11,810
Net Interest Income	(6,197)	(5,084)	(16,297)	(15,502)
Provision for credit losses	0	0	0	0
Net Interest Income After Provision for Credit Losses	(6,197)	(5,084)	(16,297)	(15,502)
Non-interest income	6,624	8,298	20,263	97,607
Non-interest expense	114,861	100,587	338,935	301,151
Internal expense transfer	(98,717)	(87,861)	(298,192)	(257,524)
Income Before Income Taxes	$ (15,717)	$ (9,512)	$ (36,777)	$ 38,478