Shareholders' Equity And Earnings Per Share (Other Comprehensive Income Reclassified from AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Gains (losses) on investment securities, net	$ 12	$ 47	$ (339)	$ (8)
Income before taxes	121,591	101,946	229,657	189,964
Income tax expense	(32,011)	(37,049)	(58,096)	(66,689)
Interest on deposits	35,293	18,471	61,842	34,741
Interest on junior subordinated debentures	2,836	2,433	5,299	4,841
Net income	89,580	64,897	171,561	123,275
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	(20)	47	(995)	(8)
Income before taxes	(20)	47	(995)	(8)
Income tax expense	8	(18)	270	3
Net income	(12)	29	(725)	(5)
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	1,339	(681)	2,019	(1,037)
Income tax expense	(360)	268	(543)	408
Interest on deposits	(1,339)	323	(2,019)	365
Interest on junior subordinated debentures	0	358	0	672
Net income	$ 979	$ (413)	$ 1,476	$ (629)