Shareholders' Equity And Earnings Per Share (Other Comprehensive Income Reclassified from AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Gains (losses) on investment securities, net	$ 90	$ 39	$ (249)	$ 31
Income before taxes	122,814	104,248	352,471	294,212
Income tax expense	(30,866)	(38,622)	(88,962)	(105,311)
Interest on deposits	48,736	23,655	110,578	58,396
Interest on junior subordinated debentures	2,940	2,640	8,239	7,481
Net income	91,948	65,626	263,509	188,901
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	1,001	39	6	31
Income before taxes	1,001	39	6	31
Income tax expense	(271)	(15)	(1)	(12)
Net income	730	24	5	19
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	2,319	(14)	4,338	(1,051)
Income tax expense	(623)	6	(1,166)	414
Interest on deposits	(2,319)	(380)	(4,338)	(15)
Interest on junior subordinated debentures	0	394	0	1,066
Net income	$ 1,696	$ (8)	$ 3,172	$ (637)