Investments (Gross Unrealized Losses and Fair Value by Length of Time for Held-To-Maturity Securities) (Detail) $ in Thousands	Jun. 30, 2015 USD ($) Securities	Dec. 31, 2014 USD ($) Securities
Schedule Of Held To Maturity Securities [Line Items]
Fair Value	$ 119,162	$ 94,805
Less than 12 months	1,407	18
More than 12 months	1,059	2,041
Total Unrealized Losses	$ 2,466	$ 2,059
Held-to-Maturity Securities
Schedule Of Held To Maturity Securities [Line Items]
Number of securities | Securities	71	49
U.S. government agencies
Schedule Of Held To Maturity Securities [Line Items]
Fair Value	$ 63,175	$ 62,778
Less than 12 months	533	0
More than 12 months	807	1,734
Total Unrealized Losses	$ 1,340	$ 1,734
U.S. government agencies | Held-to-Maturity Securities
Schedule Of Held To Maturity Securities [Line Items]
Number of securities | Securities	8	8
State and municipal
Schedule Of Held To Maturity Securities [Line Items]
Fair Value	$ 55,987	$ 32,027
Less than 12 months	874	18
More than 12 months	252	307
Total Unrealized Losses	$ 1,126	$ 325
State and municipal | Held-to-Maturity Securities
Schedule Of Held To Maturity Securities [Line Items]
Number of securities | Securities	63	41