Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Due in one year or less	$ 5,513
Due after one through five years	19,028
Due after five through ten years	29,106
Due after ten years	104,152
Available-For-Sale Securities, Debt Maturity, with Single Maturity Date, Amortized Cost, Total	157,799
Total Investment Securities	531,600
Due in one year or less	5,574
Due after one through five years	19,909
Due after five through ten years	30,906
Due after ten years	105,770
Available-For-Sale Securities, Debt Maturity, with Single Maturity Date, Fair Value, Total	162,159
Total Investment Securities	547,551
Due in one year or less	3,345
Due after one through five years	2,953
Due after five through ten years	51,873
Due after ten years	61,051
Held-To-Maturity Securities, Debt Maturities, with Single Maturity Date, Net Carrying Amount, Total	119,222
Total Investment Securities	396,770
Due in one year or less	3,345
Due after one through five years	2,979
Due after five through ten years	53,415
Due after ten years	63,732
Held-To-Maturity Securities, Debt Maturity, with Single Maturity Date, Fair Value, Total	123,471
Total Investment Securities	413,247
U.S. Government-sponsored mortgage-backed securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Without single maturity date	371,971
Without single maturity date	383,562
Without single maturity date	277,548
Without single maturity date	289,776
Equity Securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Without single maturity date	1,830
Without single maturity date	$ 1,830