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		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Unrealized Gains and Losses on Available- for-Sale Securities, Beginning balance	$ 1,662		$ 5,849
Unrealized Gains and Losses on Available- for-Sale Securities, Other comprehensive loss before reclassifications	(585)		(4,734)
Unrealized Gains and Losses on Available- for-Sale Securities, Amounts reclassified from accumulated other comprehensive loss	(53)		(91)
Unrealized Gains and Losses on Available- for-Sale Securities, Net current-period other comprehensive income (loss)	(638)		(4,825)
Unrealized Gains and Losses on Available- for-Sale Securities, Ending balance	1,024		1,024
Defined Benefit Pension Items, Beginning balance	(7,273)		(7,496)
Defined Benefit Pension Items, Other comprehensive loss before reclassifications
Defined Benefit Pension Items, Amounts reclassified from accumulated other comprehensive loss	119		342
Defined Benefit Pension Items, Net current-period other comprehensive income (loss)	119		342
Defined Benefit Pension Items, Ending balance	(7,154)		(7,154)
Beginning balance	(5,611)		(1,647)
Other comprehensive loss before reclassifications	(585)		(4,734)
Amounts reclassified from accumulated other comprehensive loss	66		251
Total other comprehensive income (loss)	(519)	558	(4,483)	1,059
Ending balance	$ (6,130)		$ (6,130)