Investment Securities - 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	Dec. 31, 2012
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Due in one year or less	$ 4,366
Due after one through five years	14,764
Due after five through ten years	54,148
Due after ten years	85,489
Available-For-Sale Securities, Debt Maturity, with Single Maturity Date, Amortized Cost, Total	158,767
Total Investment Securities	498,104
Due in one year or less	4,415
Due after one through five years	15,468
Due after five through ten years	57,442
Due after ten years	85,733
Available-For-Sale Securities, Debt Maturity, with Single Maturity Date, Fair Value, Total	163,058
Total Investment Securities	513,343
Due in one year or less	2,590
Due after one through five years	2,554
Due after five through ten years	57,811
Due after ten years	54,272
Held-To-Maturity Securities, Debt Maturities, with Single Maturity Date, Net Carrying Amount, Total	117,227
Total Investment Securities	361,020
Due in one year or less	2,594
Due after one through five years	2,575
Due after five through ten years	60,163
Due after ten years	57,383
Held-To-Maturity Securities, Debt Maturity, with Single Maturity Date, Fair Value, Total	122,715
Total Investment Securities	378,174
U.S. Government-sponsored mortgage-backed securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Without single maturity date	337,631
Without single maturity date	348,579
Without single maturity date	243,793
Without single maturity date	255,459
Equity securities
Schedule of Available for sale Securities and Held to maturity Securities [Line Items]
Without single maturity date	1,706
Without single maturity date	1,706
Without single maturity date
Without single maturity date