Investment Securities (Detail) - Amortized cost, gross unrealized gains and losses, and estimated fair value on investment securities (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2011
Amortized Cost	$ 256,581	$ 407,654	$ 406,665
Gross Unrealized Gains	4,524	7,135	11,923
Gross Unrealized Losses	7,307	10,239	6,480
Estimated Fair Value	253,798	404,550	412,108
Amortized Cost	15,555	20,486	21,671
Gross Unrealized Gains	2,312	2,756	2,491
Gross Unrealized Losses	0	0	0
Estimated Fair Value	17,867	23,242	24,162
Amortized Cost	20,914	32,694	35,782
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Estimated Fair Value	20,914	32,694	35,782
State And Municipal Obligations [Member]
Amortized Cost	15,055	19,978	20,863
Gross Unrealized Gains	2,312	2,756	2,491
Gross Unrealized Losses	0	0	0
Estimated Fair Value	17,367	22,734	23,354
Certificates of Deposit [Member]
Amortized Cost	500	508	808
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Estimated Fair Value	500	508	808
US Government Agencies And Corporations [Member]
Amortized Cost	1,260	1,790	1,826
Gross Unrealized Gains	18	33	37
Gross Unrealized Losses	0	0	0
Estimated Fair Value	1,278	1,823	1,863
State And Municipal Obligations [Member]
Amortized Cost	13,460	450	450
Gross Unrealized Gains	84	38	31
Gross Unrealized Losses	61	0	0
Estimated Fair Value	13,483	488	481
Collateralized Debt Obligations [Member]
Amortized Cost	6,191	7,012	7,127
Gross Unrealized Gains	156	0	0
Gross Unrealized Losses	3,015	3,765	4,053
Estimated Fair Value	3,332	3,247	3,074
Mortgage Backed Securities Excluding Collateralized Mortgage Obligations [Member]
Amortized Cost	72,527	80,696	85,306
Gross Unrealized Gains	1,928	3,719	3,668
Gross Unrealized Losses	151	16	17
Estimated Fair Value	74,304	84,399	88,957
Collateralized Mortgage Obligations [Member]
Amortized Cost	157,534	312,124	306,525
Gross Unrealized Gains	1,249	3,289	8,117
Gross Unrealized Losses	3,900	6,118	2,129
Estimated Fair Value	154,883	309,295	312,513
Other Securities [Member]
Amortized Cost	5,609	5,582	5,431
Gross Unrealized Gains	1,089	56	70
Gross Unrealized Losses	180	340	281
Estimated Fair Value	6,518	5,298	5,220
Federal Home Loan Bank Stock [Member]
Amortized Cost	16,343	32,694	35,782
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Estimated Fair Value	16,343	32,694	35,782
Federal Reserve Bank Stock [Member]
Amortized Cost	4,571	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Estimated Fair Value	$ 4,571	$ 0	$ 0