Investments - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Available for sale securities:
Available for sale securities, Due in one year or less, Amortized Cost	$ 13,898
Available for sale securities, Due after one year through five years, Amortized Cost	63,157
Available for sale securities, Due after five year through ten years, Amortized Cost	72,436
Available for sale securities, Due after ten years, Amortized Cost	95,260
Available for sale securities, Mortgage-backed securities, Amortized Cost	42,764
Totals, Amortized Cost	287,515
Available for sale securities, Due in one year or less, Fair Value	13,998
Available for sale securities, Due after one year through five years, Fair Value	63,282
Available for sale securities, Due after five years through ten years, Fair Value	72,389
Available for sale securities, Due after ten years, Fair Value	90,134
Available for sale securities, Mortgage-backed securities, Fair value	41,865
Totals, Fair Value	281,668
Held to maturity securities:
Held to maturity securities, Due in one year or less, Amortized Cost	1,013
Held to maturity securities, Due after one year through five years, Amortized Cost	1,777
Held to maturity securities, Due after five years through ten years, Amortized Cost	3,492
Held to maturity securities, Due after ten years, Amortized Cost	3,450
Totals, Amortized Cost	9,732	7,125
Held to maturity securities, Due in one year or less, Fair Value	1,022
Held to maturity securities, Due after one year through five years, Fair Value	1,773
Held to maturity securities, Due after five years through ten years, Fair Value	3,353
Held to maturity securities, Due after ten years, Fair Value	3,130
Totals, Fair Value	$ 9,278	$ 7,225