Shareholders' Equity And Earnings Per Share (Other Comprehensive Income Reclassified from AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before taxes	$ 137,284	$ 134,601	$ 255,070	$ 363,419
Income tax expense	(29,969)	(35,480)	(63,284)	(93,686)
Interest on deposits	39,084	76,168	156,576	204,168
Interest on junior subordinated debentures	2,703	2,897	8,266	9,111
Net income	107,315	99,121	191,786	269,733
Reclassification Out of Accumulated Other Comprehensive Income | Accumulated Unrealized Losses on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Gains (losses) on investment securities, net	50	400	200	856
Income before taxes	50	400	200	856
Income tax expense	(14)	(108)	(54)	(230)
Net income	36	292	146	626
Reclassification Out of Accumulated Other Comprehensive Income | Accumulated Unrealized Gains on Derivative Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income before taxes	(5,667)	2,428	(12,208)	10,071
Income tax expense	1,510	(647)	3,254	(2,685)
Interest on deposits	3,884	(2,635)	8,806	(10,403)
Interest on other borrowings	740	196	1,458	321
Interest on junior subordinated debentures	1,043	11	1,944	11
Net income	$ (4,157)	$ 1,781	$ (8,954)	$ 7,386