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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 943	$ (5,611)	$ (4,247)	$ (1,647)
Other comprehensive income (loss) before reclassifications	406	(585)	5,582	(4,734)
Amounts reclassified from accumulated other comprehensive income (loss)	57	66	71	251
Total other comprehensive income (loss)	463	(519)	5,653	(4,483)
Ending balance	1,406	(6,130)	1,406	(6,130)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	2,777	1,662	341	5,849
Other comprehensive income (loss) before reclassifications	406	(585)	2,916	(4,734)
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	(53)	(75)	(91)
Total other comprehensive income (loss)	405	(638)	2,841	(4,825)
Ending balance	3,182	1,024	3,182	1,024
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(1,834)	(7,273)	(4,588)	(7,496)
Other comprehensive income (loss) before reclassifications			2,666
Amounts reclassified from accumulated other comprehensive income (loss)	58	119	146	342
Total other comprehensive income (loss)	58	119	2,812	342
Ending balance	$ (1,776)	$ (7,154)	$ (1,776)	$ (7,154)