Shareholders' Equity And Earnings Per Share (Other Comprehensive Income Reclassified from AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Gains (losses) on investment securities, net	$ 47	$ 1,440	$ (8)	$ 2,765
Interest on deposits	18,471	13,594	34,741	26,375
Interest on junior subordinated debentures	2,433	2,353	4,841	4,573
Income before taxes	101,946	79,971	189,964	158,468
Income tax expense	(37,049)	(29,930)	(66,689)	(59,316)
Net income	64,897	50,041	123,275	99,152
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accumulated Unrealized Gains (Losses) on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Gains (losses) on investment securities, net	47	1,440	(8)	2,765
Income before taxes	47	1,440	(8)	2,765
Income tax expense	(18)	(565)	3	(1,086)
Net income	29	875	(5)	1,679
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accumulated Unrealized Losses on Derivative Instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Interest on deposits	323	338	365	593
Interest on junior subordinated debentures	358	494	672	962
Income before taxes	(681)	(832)	(1,037)	(1,555)
Income tax expense	268	327	408	611
Net income	$ (413)	$ (505)	$ (629)	$ (944)