Securities (Detail) - Securities Portfolio - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Securities Available-for-Sale
Amortized Cost	$ 1,324,146	$ 1,192,322
Gross Unrealized Gains	9,921	17,922
Gross Unrealized Losses	(27,431)	(23,235)
Fair Value	1,306,636	1,187,009
Securities Held-to-Maturity
Amortized Cost	23,152	26,555
Gross Unrealized Gains	0	1,115
Gross Unrealized Losses	(3,098)	0
Fair Value	20,054	27,670
Trading Securities	16,894	17,460
US Treasury Securities
Securities Available-for-Sale
Amortized Cost	17,000	0
Gross Unrealized Gains	15	0
Gross Unrealized Losses	(35)	0
Fair Value	16,980	0
U.S. Agency Securities
Securities Available-for-Sale
Amortized Cost	86,461	30,297
Gross Unrealized Gains	351	144
Gross Unrealized Losses	(169)	(10)
Fair Value	86,643	30,431
Collateralized Mortgage Obligations
Securities Available-for-Sale
Amortized Cost	695,198	538,882
Gross Unrealized Gains	1,072	2,256
Gross Unrealized Losses	(9,085)	(6,982)
Fair Value	687,185	534,156
Other Mortgage Backed Securities
Securities Available-for-Sale
Amortized Cost	152,481	155,443
Gross Unrealized Gains	1,920	4,632
Gross Unrealized Losses	(871)	(310)
Fair Value	153,530	159,765
Municipal Securities
Securities Available-for-Sale
Amortized Cost	321,437	414,255
Gross Unrealized Gains	6,443	10,583
Gross Unrealized Losses	(310)	(1,018)
Fair Value	327,570	423,820
Trust-preferred Collateralized Debt Obligations
Securities Available-for-Sale
Amortized Cost	48,287	48,502
Gross Unrealized Gains	34	152
Gross Unrealized Losses	(16,792)	(14,880)
Fair Value	31,529	33,774
Corporate Debt Securities
Securities Available-for-Sale
Amortized Cost	0	1,719
Gross Unrealized Gains	0	83
Gross Unrealized Losses	0	0
Fair Value	0	1,802
Equity Securities
Securities Available-for-Sale
Amortized Cost	3,282	3,224
Gross Unrealized Gains	86	72
Gross Unrealized Losses	(169)	(35)
Fair Value	$ 3,199	$ 3,261

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