Amortized Cost and Aggregate Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Available-for-sale securities
Due within one year, Amortized Cost	$ 66,702
Due after one year but within five years, Amortized Cost	3,118
Due after five years but within ten years, Amortized Cost	91,013
Due after ten years, Amortized Cost	111,713
Amortized Cost	325,430	$ 372,389
Held-to-maturity securities
Due within one year, Amortized Cost	46,890
Due after one year but within five years, Amortized Cost	25,349
Due after five years but within ten years, Amortized Cost	0
Due after ten years, Amortized Cost	0
Held-to-maturity Securities, Amortized Cost	72,239	72,541
Available-for-sale securities
Due within one year, Fair Value	66,684
Due after one year but within five years, Fair Value	3,189
Due after five years but within ten years, Fair Value	95,908
Due after ten years, Fair Value	103,695
Fair Value	322,699	366,173
Held-to-maturity securities
Due within one year, Fair Value	46,948
Due after one year but within five years, Fair Value	25,858
Due after five years but within ten years, Fair Value	0
Due after ten years, Fair Value	0
Fair Value	72,806	72,490
Debt Securities
Available-for-sale securities
Amortized Cost	272,546
Available-for-sale securities
Fair Value	269,476
Total Mortgage Backed Securities
Available-for-sale securities
Amortized Cost	52,829
Available-for-sale securities
Fair Value	53,150
Equity Securities
Available-for-sale securities
Amortized Cost	55	66
Available-for-sale securities
Fair Value	$ 73	$ 72