Securities Available-for Sale - Schedule of Amortized Cost and Fair Value of Securities Available-for-Sale (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Due in one year or less, Amortized Cost	$ 55,559	$ 52,769
Due after one year through 5 years, Amortized Cost	182,156	199,757
Due after 5 years through 10 years, Amortized Cost	138,243	86,479
Due after 10 years, Amortized Cost	4,496	1,777
Amortized Cost	380,454	340,782
Due in one year or less, Estimated Fair Value	55,690	52,757
Due after one year through 5 years, Estimated Fair Value	185,857	202,889
Due after 5 years through 10 years, Estimated Fair Value	143,698	89,043
Due after 10 years, Estimated Fair Value	4,640	1,853
Estimated Fair Value	$ 389,885	$ 346,542