Debt and Equity Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 Security	Dec. 31, 2013 Security
Held To Maturity Debt Securities [Line Items]
Held to Maturity Securities, Fair Value, Less than 12 Month	$ 1,111	$ 14,495
Held to Maturity Securities, Unrealized losses, Less than 12 Month	4	751
Held to Maturity Securities, Number of securities included, Less than 12 Month	3	26
Held to Maturity Securities, Fair Value, 12 Month or More	10,958	343
Held to Maturity Securities, Unrealized losses, 12 Month or More	384	8
Held to Maturity Securities, Number of securities included, 12 Month or More	16	2
Held to Maturity Securities, Total Fair Value	12,069	14,838
Held to Maturity Securities, Total Unrealized Losses	388	759
Available-for-Sale Securities, Fair Value, Less than 12 Month	158,820	211,684
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	1,463	5,902
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month	65	83
Available-for-Sale Securities, Fair Value, 12 Month or More	112,914	26,111
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	3,052	1,949
Available-for-Sale Securities, Number of securities included, 12 Month or More	57	23
Available-for-Sale Securities, Total Fair Value	271,734	237,795
Available-for-Sale Securities, Total Unrealized Losses	4,515	7,851
US Government-Sponsored Enterprises (GSEs) [Member]
Held To Maturity Debt Securities [Line Items]
Available-for-Sale Securities, Fair Value, Less than 12 Month	44,030	103,502
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	343	4,289
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month	15	32
Available-for-Sale Securities, Fair Value, 12 Month or More	85,021	19,479
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	2,412	1,603
Available-for-Sale Securities, Number of securities included, 12 Month or More	28	7
Available-for-Sale Securities, Total Fair Value	129,051	122,981
Available-for-Sale Securities, Total Unrealized Losses	2,755	5,892
Government- Sponsored Enterprises (GSEs) Residential Mortgage Backed [Member]
Held To Maturity Debt Securities [Line Items]
Held to Maturity Securities, Fair Value, Less than 12 Month		6,678
Held to Maturity Securities, Unrealized losses, Less than 12 Month		520
Held to Maturity Securities, Number of securities included, Less than 12 Month		5
Held to Maturity Securities, Fair Value, 12 Month or More	6,775
Held to Maturity Securities, Unrealized losses, 12 Month or More	310
Held to Maturity Securities, Number of securities included, 12 Month or More	6
Held to Maturity Securities, Total Fair Value	6,775	6,678
Held to Maturity Securities, Total Unrealized Losses	310	520
Available-for-Sale Securities, Fair Value, Less than 12 Month	92,184	97,805
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	847	1,449
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month	35	32
Available-for-Sale Securities, Fair Value, 12 Month or More	22,462	1,866
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	461	32
Available-for-Sale Securities, Number of securities included, 12 Month or More	14	2
Available-for-Sale Securities, Total Fair Value	114,646	99,671
Available-for-Sale Securities, Total Unrealized Losses	1,308	1,481
Obligations of States and Political Subdivisions [Member]
Held To Maturity Debt Securities [Line Items]
Held to Maturity Securities, Fair Value, Less than 12 Month	1,111	7,817
Held to Maturity Securities, Unrealized losses, Less than 12 Month	4	231
Held to Maturity Securities, Number of securities included, Less than 12 Month	3	21
Held to Maturity Securities, Fair Value, 12 Month or More	4,183	343
Held to Maturity Securities, Unrealized losses, 12 Month or More	74	8
Held to Maturity Securities, Number of securities included, 12 Month or More	10	2
Held to Maturity Securities, Total Fair Value	5,294	8,160
Held to Maturity Securities, Total Unrealized Losses	78	239
Available-for-Sale Securities, Fair Value, Less than 12 Month	1,602	5,645
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	7	95
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month	3	14
Available-for-Sale Securities, Fair Value, 12 Month or More	5,431	4,766
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	179	314
Available-for-Sale Securities, Number of securities included, 12 Month or More	15	14
Available-for-Sale Securities, Total Fair Value	7,033	10,411
Available-for-Sale Securities, Total Unrealized Losses	186	409
SBAP Member
Held To Maturity Debt Securities [Line Items]
Available-for-Sale Securities, Fair Value, Less than 12 Month	21,004	4,732
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	266	69
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month	12	5
Available-for-Sale Securities, Fair Value, 12 Month or More
Available-for-Sale Securities, Unrealized Loss, 12 Month or More
Available-for-Sale Securities, Number of securities included, 12 Month or More
Available-for-Sale Securities, Total Fair Value	21,004	4,732
Available-for-Sale Securities, Total Unrealized Losses	$ 266	$ 69