Other Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Income Loss, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (47)	$ (4,247)
Other comprehensive income before reclassifications	585	1,318
Amounts reclassified from accumulated other comprehensive income (loss)	46	25
Total other comprehensive income	631	1,343
Ending balance	584	(2,904)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	3,730	341
Other comprehensive income before reclassifications	585	1,318
Amounts reclassified from accumulated other comprehensive income (loss)		(3)
Total other comprehensive income	585	1,315
Ending balance	4,315	1,656
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(3,777)	(4,588)
Amounts reclassified from accumulated other comprehensive income (loss)	46	28
Total other comprehensive income	46	28
Ending balance	$ (3,731)	$ (4,560)