Amortized Cost and Fair Value of Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Securities Available-for-Sale: Amortized cost
Due in one year or less	$ 3,145
Due after one year through five years	13,191
Due after five years through ten years	51,937
Due after ten years	26,649
Total	571,058	500,128
Securities Available-for-Sale, Fair Value
Due in one year or less	3,162
Due after one year through five years	13,570
Due after five years through ten years	54,239
Due after ten years	28,986
Total	587,602	516,844
Securities Held-to-Maturity, Carrying Amount
Due in one year or less	0
Due after one year through five years	346
Due after five years through ten years	0
Due after ten years	0
Total	346	690
Securities Held-to-Maturity, Fair Value
Due in one year or less	0
Due after one year through five years	351
Due after five years through ten years	0
Due after ten years	0
Fair Value	351	697
Mortgage-backed Securities - Residential [Member]
Securities Available-for-Sale: Amortized cost
Available-for-Sale, amortized cost	475,452
Total	475,452	431,495
Securities Available-for-Sale, Fair Value
Available-for-Sale, Fair Value	486,912
Total	486,912	443,934
Equity Securities [Member]
Securities Available-for-Sale: Amortized cost
Available-for-Sale, amortized cost	684
Total	684	684
Securities Available-for-Sale, Fair Value
Available-for-Sale, Fair Value	733
Total	$ 733	$ 684