Securities - Amortized Cost and Fair Value of Securities Available for Sale and Held for Investment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	$ 661,862	$ 637,940
Gross Unrealized Gains, Securities Available for Sale	3,576	7,011
Gross Unrealized Losses, Securities Available for Sale	(14,993)	(1,901)
Fair Value, Securities Available for Sale	650,445	643,050
Gross Amortized Cost, Securities Held for Investment		13,818
Gross Unrealized Gains, Securities Held for Investment		819
Gross Unrealized Losses, Securities Held for Investment		(95)
Fair value, Securities Held for Investment		14,542
U.S. Treasury Securities and Obligations of U.S. Government Sponsored Entities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	101	1,700
Gross Unrealized Gains, Securities Available for Sale	0	7
Gross Unrealized Losses, Securities Available for Sale	0	0
Fair Value, Securities Available for Sale	101	1,707
Mortgage-Backed Securities of U.S. Government Sponsored Entities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	136,184	186,404
Gross Unrealized Gains, Securities Available for Sale	1,534	3,320
Gross Unrealized Losses, Securities Available for Sale	(3,676)	(469)
Fair Value, Securities Available for Sale	134,042	189,255
Collateralized Mortgage Obligations of U.S. Government Sponsored Entities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	385,832	352,731
Gross Unrealized Gains, Securities Available for Sale	835	2,430
Gross Unrealized Losses, Securities Available for Sale	(10,144)	(902)
Fair Value, Securities Available for Sale	376,523	354,259
Gross Amortized Cost, Securities Held for Investment		4,687
Gross Unrealized Gains, Securities Held for Investment		0
Gross Unrealized Losses, Securities Held for Investment		(92)
Fair value, Securities Held for Investment		4,595
Privately Mortgage Backed Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	29,754
Gross Unrealized Gains, Securities Available for Sale	0
Gross Unrealized Losses, Securities Available for Sale	(642)
Fair Value, Securities Available for Sale	29,112
Private Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	70,845	96,258
Gross Unrealized Gains, Securities Available for Sale	903	1,203
Gross Unrealized Losses, Securities Available for Sale	(297)	(530)
Fair Value, Securities Available for Sale	71,451	96,931
Gross Amortized Cost, Securities Held for Investment		1,278
Gross Unrealized Gains, Securities Held for Investment		33
Gross Unrealized Losses, Securities Held for Investment		0
Fair value, Securities Held for Investment		1,311
Collateralized Loan Obligations [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	32,560
Gross Unrealized Gains, Securities Available for Sale	0
Gross Unrealized Losses, Securities Available for Sale	(226)
Fair Value, Securities Available for Sale	32,334
Obligations of State and Political Subdivisions [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Available for Sale	6,586	847
Gross Unrealized Gains, Securities Available for Sale	304	51
Gross Unrealized Losses, Securities Available for Sale	(8)	0
Fair Value, Securities Available for Sale	6,882	898
Gross Amortized Cost, Securities Held for Investment		6,353
Gross Unrealized Gains, Securities Held for Investment		737
Gross Unrealized Losses, Securities Held for Investment		(3)
Fair value, Securities Held for Investment		7,087
Other [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Gross Amortized Cost, Securities Held for Investment		1,500
Gross Unrealized Gains, Securities Held for Investment		49
Gross Unrealized Losses, Securities Held for Investment		0
Fair value, Securities Held for Investment		$ 1,549