Business Segments - Schedule of Financial Data for Business Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Average interest earning assets	$ 37,778,387	$ 29,877,384	$ 36,226,232	$ 29,721,015
Interest income	348,525	327,742	712,318	647,966
Interest expense	65,966	107,508	164,420	209,084
Net Interest Income	282,559	220,234	547,898	438,882
Provision for credit losses	41,156	2,100	75,839	10,100
Net Interest Income After Provision for Credit Losses	241,403	218,134	472,059	428,782
Non-interest income	44,830	27,603	86,227	135,276
Non-interest expense	157,166	141,737	312,822	289,532
Internal expense transfer	0	0	0	0
Income Before Income Taxes	$ 129,067	$ 104,000	$ 245,464	$ 274,526
Return on average interest earning assets (pre-tax)	1.37%	1.39%	1.36%	1.85%
Consumer Lending
Segment Reporting Information [Line Items]
Average interest earning assets	$ 7,214,368	$ 6,756,322	$ 7,215,756	$ 6,788,511
Interest income	66,807	67,617	135,062	135,644
Interest expense	11,469	23,428	31,169	45,952
Net Interest Income	55,338	44,189	103,893	89,692
Provision for credit losses	3,106	885	9,891	2,983
Net Interest Income After Provision for Credit Losses	52,232	43,304	94,002	86,709
Non-interest income	17,175	13,037	31,852	26,819
Non-interest expense	20,440	18,392	40,311	37,097
Internal expense transfer	19,406	19,291	39,741	38,718
Income Before Income Taxes	$ 29,561	$ 18,658	$ 45,802	$ 37,713
Return on average interest earning assets (pre-tax)	1.64%	1.10%	1.27%	1.11%
Commercial Lending
Segment Reporting Information [Line Items]
Average interest earning assets	$ 24,826,832	$ 18,796,093	$ 23,804,558	$ 18,615,885
Interest income	255,152	229,366	520,027	449,650
Interest expense	40,640	65,141	102,826	126,012
Net Interest Income	214,512	164,225	417,201	323,638
Provision for credit losses	38,009	1,215	65,148	7,117
Net Interest Income After Provision for Credit Losses	176,503	163,010	352,053	316,521
Non-interest income	16,172	7,688	31,771	14,470
Non-interest expense	23,250	26,324	47,408	51,568
Internal expense transfer	66,858	53,722	131,054	106,259
Income Before Income Taxes	$ 102,567	$ 90,652	$ 205,362	$ 173,164
Return on average interest earning assets (pre-tax)	1.65%	1.93%	1.73%	1.86%
Investment Management
Segment Reporting Information [Line Items]
Average interest earning assets	$ 5,737,187	$ 4,324,969	$ 5,205,918	$ 4,316,619
Interest income	27,623	31,966	59,392	65,190
Interest expense	9,728	14,994	22,488	29,220
Net Interest Income	17,895	16,972	36,904	35,970
Provision for credit losses	41	0	800	0
Net Interest Income After Provision for Credit Losses	17,854	16,972	36,104	35,970
Non-interest income	5,823	2,560	8,965	4,678
Non-interest expense	642	216	1,029	303
Internal expense transfer	15,505	12,399	28,680	24,686
Income Before Income Taxes	$ 7,530	$ 6,917	$ 15,360	$ 15,659
Return on average interest earning assets (pre-tax)	0.52%	0.64%	0.59%	0.73%
Corporate and Other Adjustments
Segment Reporting Information [Line Items]
Average interest earning assets	$ 0	$ 0	$ 0	$ 0
Interest income	(1,057)	(1,207)	(2,163)	(2,518)
Interest expense	4,129	3,945	7,937	7,900
Net Interest Income	(5,186)	(5,152)	(10,100)	(10,418)
Provision for credit losses	0	0	0	0
Net Interest Income After Provision for Credit Losses	(5,186)	(5,152)	(10,100)	(10,418)
Non-interest income	5,660	4,318	13,639	89,309
Non-interest expense	112,834	96,805	224,074	200,564
Internal expense transfer	(101,769)	(85,412)	(199,475)	(169,663)
Income Before Income Taxes	$ (10,591)	$ (12,227)	$ (21,060)	$ 47,990