Debt and Equity Securities - Gross Unrealized Losses and Fair Value of Company's Investments (Detail) $ in Thousands	Jun. 30, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security
Held To Maturity Debt Securities [Line Items]
Held to Maturity Securities, Fair Value, Less than 12 Month	$ 10,813
Held to Maturity Securities, Unrealized losses, Less than 12 Month	$ 108
Held to Maturity Securities, Number of securities included, Less than 12 Month | Security	25
Held to Maturity Securities, Fair Value, 12 Month or More	$ 3,294	$ 7,251
Held to Maturity Securities, Unrealized losses, 12 Month or More	$ 170	$ 188
Held to Maturity Securities, Number of securities included, 12 Month or More | Security	4	10
Held to Maturity Securities, Total Fair Value	$ 14,107	$ 7,251
Held to Maturity Securities, Total Unrealized Losses	278	188
Available-for-Sale Securities, Fair Value, Less than 12 Month	148,513	119,449
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	$ 1,133	$ 635
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month | Security	96	59
Available-for-Sale Securities, Fair Value, 12 Month or More	$ 57,005	$ 101,121
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	$ 885	$ 1,521
Available-for-Sale Securities, Number of securities included, 12 Month or More | Security	32	50
Available-for-Sale Securities, Total Fair Value	$ 205,518	$ 220,570
Available-for-Sale Securities, Total Unrealized Losses	2,018	2,156
US Government-Sponsored Enterprises (GSEs) and Agency-Backed Securities [Member]
Held To Maturity Debt Securities [Line Items]
Available-for-Sale Securities, Fair Value, Less than 12 Month	29,940	34,753
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	$ 151	$ 143
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month | Security	11	10
Available-for-Sale Securities, Fair Value, 12 Month or More	$ 46,605	$ 74,250
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	$ 636	$ 1,186
Available-for-Sale Securities, Number of securities included, 12 Month or More | Security	14	24
Available-for-Sale Securities, Total Fair Value	$ 76,545	$ 109,003
Available-for-Sale Securities, Total Unrealized Losses	787	1,329
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	1,574
Held to Maturity Securities, Unrealized losses, Less than 12 Month	$ 25
Held to Maturity Securities, Number of securities included, Less than 12 Month | Security	1
Held to Maturity Securities, Fair Value, 12 Month or More	$ 2,996	4,674
Held to Maturity Securities, Unrealized losses, 12 Month or More	$ 166	$ 147
Held to Maturity Securities, Number of securities included, 12 Month or More | Security	3	4
Held to Maturity Securities, Total Fair Value	$ 4,570	$ 4,674
Held to Maturity Securities, Total Unrealized Losses	191	147
Available-for-Sale Securities, Fair Value, Less than 12 Month	91,809	66,504
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	$ 756	$ 279
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month | Security	46	36
Available-for-Sale Securities, Fair Value, 12 Month or More	$ 4,414	$ 22,172
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	$ 101	$ 185
Available-for-Sale Securities, Number of securities included, 12 Month or More | Security	8	13
Available-for-Sale Securities, Total Fair Value	$ 96,223	$ 88,676
Available-for-Sale Securities, Total Unrealized Losses	857	464
SBAP [Member]
Held To Maturity Debt Securities [Line Items]
Available-for-Sale Securities, Fair Value, Less than 12 Month	14,692	16,114
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	$ 103	$ 205
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month | Security	7	9
Available-for-Sale Securities, Fair Value, 12 Month or More	$ 2,722
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	$ 19
Available-for-Sale Securities, Number of securities included, 12 Month or More | Security	1
Available-for-Sale Securities, Total Fair Value	$ 17,414	$ 16,114
Available-for-Sale Securities, Total Unrealized Losses	122	205
Obligations of States and Political Subdivisions [Member]
Held To Maturity Debt Securities [Line Items]
Held to Maturity Securities, Fair Value, Less than 12 Month	9,239
Held to Maturity Securities, Unrealized losses, Less than 12 Month	$ 83
Held to Maturity Securities, Number of securities included, Less than 12 Month | Security	24
Held to Maturity Securities, Fair Value, 12 Month or More	$ 298	2,577
Held to Maturity Securities, Unrealized losses, 12 Month or More	$ 4	$ 41
Held to Maturity Securities, Number of securities included, 12 Month or More | Security	1	6
Held to Maturity Securities, Total Fair Value	$ 9,537	$ 2,577
Held to Maturity Securities, Total Unrealized Losses	87	41
Available-for-Sale Securities, Fair Value, Less than 12 Month	12,072	2,078
Available-for-Sale Securities, Unrealized Losses, Less than 12 Month	$ 123	$ 8
Available-for-Sale Securities, Number of Securities Included, Less than 12 Month | Security	32	4
Available-for-Sale Securities, Fair Value, 12 Month or More	$ 3,264	$ 4,699
Available-for-Sale Securities, Unrealized Loss, 12 Month or More	$ 129	$ 150
Available-for-Sale Securities, Number of securities included, 12 Month or More | Security	9	13
Available-for-Sale Securities, Total Fair Value	$ 15,336	$ 6,777
Available-for-Sale Securities, Total Unrealized Losses	$ 252	$ 158