Shareholders' Equity and Earnings Per Share Shareholders' Equity And Earnings Per Share (Other Comprehensive Income Reclassified from AOCI) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
(Losses) gains on available-for-sale securities, net	$ (98)	$ (153)	$ 402	$ (522)
Interest on deposits	12,436	12,298	36,246	35,980
Interest on junior subordinated debentures	2,124	2,091	6,034	6,137
Income before taxes	62,197	65,258	195,358	184,629
Income tax expense	(23,842)	(25,034)	(74,120)	(71,364)
Net income	38,355	40,224	121,238	113,265
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accumulated Unrealized Losses on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
(Losses) gains on available-for-sale securities, net	(98)	(153)	402	(522)
Income before taxes	(98)	(153)	402	(522)
Income tax expense	38	62	(158)	208
Net income	(60)	(91)	244	(314)
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	92	0	92	0
Interest on junior subordinated debentures	479	553	1,350	1,567
Income before taxes	(571)	(553)	(1,442)	(1,567)
Income tax expense	224	220	565	623
Net income	$ (347)	$ (333)	$ (877)	$ (944)