Investments (Gross Unrealized Losses and Fair Value by Length of Time for Held-To-Maturity Securities) (Detail) $ in Thousands	Sep. 30, 2015 USD ($) Securities	Dec. 31, 2014 USD ($) Securities
Schedule Of Held To Maturity Securities [Line Items]
Fair Value	$ 76,010	$ 94,805
Less than 12 months	345	18
More than 12 months	388	2,041
Total Unrealized Losses	$ 733	$ 2,059
Held-to-Maturity Securities
Schedule Of Held To Maturity Securities [Line Items]
Number of securities | Securities	34	49
U.S. government agencies
Schedule Of Held To Maturity Securities [Line Items]
Fair Value	$ 51,050	$ 62,778
Less than 12 months	208	0
More than 12 months	202	1,734
Total Unrealized Losses	$ 410	$ 1,734
U.S. government agencies | Held-to-Maturity Securities
Schedule Of Held To Maturity Securities [Line Items]
Number of securities | Securities	5	8
State and municipal
Schedule Of Held To Maturity Securities [Line Items]
Fair Value	$ 24,960	$ 32,027
Less than 12 months	137	18
More than 12 months	186	307
Total Unrealized Losses	$ 323	$ 325
State and municipal | Held-to-Maturity Securities
Schedule Of Held To Maturity Securities [Line Items]
Number of securities | Securities	29	41