Other Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Loss, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (2,904)	$ (1,966)	$ (4,247)	$ (1,647)
Other comprehensive income (loss) before reclassifications	3,859	(3,737)	5,176	(4,149)
Amounts reclassified from accumulated other comprehensive loss	(12)	92	14	185
Total other comprehensive income (loss)	3,847	(3,645)	5,190	(3,964)
Ending balance	943	(5,611)	943	(5,611)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	1,655	5,426	341	5,849
Other comprehensive income (loss) before reclassifications	1,193	(3,737)	2,510	(4,149)
Amounts reclassified from accumulated other comprehensive loss	(71)	(27)	(74)	(38)
Total other comprehensive income (loss)	1,122	(3,764)	2,436	(4,187)
Ending balance	2,777	1,662	2,777	1,662
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4,559)	(7,392)	(4,588)	(7,496)
Other comprehensive income (loss) before reclassifications	2,666		2,666
Amounts reclassified from accumulated other comprehensive loss	59	119	88	223
Total other comprehensive income (loss)	2,725	119	2,754	223
Ending balance	$ (1,834)	$ (7,273)	$ (1,834)	$ (7,273)