Condensed Statements of Income for Parent Company (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
INCOME:
Gain (loss) on sale of securities, net									$ 2,907	$ 414	$ 4,072
OPERATING EXPENSE:
Salaries and employee benefits									16,530	15,557	14,712
INCOME BEFORE INCOME TAXES	2,201	1,868	1,535	2,906	1,631	1,908	2,068	1,574	8,510	7,180	3,040
INCOME TAX BENEFIT	647	481	561	567	102	414	503	288	2,256	1,306	34
Net income	1,554	1,387	974	2,339	1,529	1,494	1,565	1,286	6,254	5,874	3,006
Parent Company
INCOME:
Dividends from subsidiaries									42,372	21,661	19,500
Interest income from securities									68	98	247
ESOP loan interest income									813	848	884
Gain (loss) on sale of securities, net										134	(22)
Other income										1	2
Total income									43,253	22,742	20,611
OPERATING EXPENSE:
Salaries and employee benefits									2,262	2,670	2,710
ESOP interest expense									813	848	884
Other									511	762	426
Total operating expense									3,586	4,280	4,020
INCOME BEFORE EQUITY IN UNDISTRIBUTED INCOME OF SUBSIDIARIES AND INCOME TAXES									39,667	18,462	16,591
DIVIDENDS IN EXCESS OF EARNINGS OF SUBSIDIARIES									(34,130)	(13,237)	(13,600)
INCOME BEFORE INCOME TAXES									5,537	5,225	2,991
INCOME TAX BENEFIT									(717)	(649)	(15)
Net income									$ 6,254	$ 5,874	$ 3,006