Accumulated Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Equity [Abstract]
Beginning Balance, Defined Benefit Pension Plan			$ (21,401)	$ (15,155)
Defined Benefit Pension Plan, Other comprehensive income before reclassifications
Defined Benefit Pension Plan, Amounts reclassified from accumulated other comprehensive income	575	365	1,050	674
Defined Benefit Pension Plan, Period change			1,050	674
Ending Balance, Defined Benefit Pension Plan	(20,351)	(14,481)	(20,351)	(14,481)
Beginning balance, Unrealized Gains (Losses) on Securities Available-for-Sale			13,032	11,292
Unrealized Gains (Losses) on Securities Available-for-Sale, Other comprehensive income before reclassifications			(11,526)	579
Unrealized Gains (Losses) on Securities Available-for-Sale, Amounts reclassified from accumulated other comprehensive income	(71)	(619)	(82)	(682)
Unrealized Gains (Losses) on Securities Available-for-Sale, Period change			(11,608)	(103)
Ending balance, Unrealized Gains (Losses) on Securities Available-for-Sale	1,424	11,189	1,424	11,189
Beginning balance, Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity			2,004	2,961
Unrealized Gains (Losses) on Securities Transferred from Available-for-Sale to Held-to-maturity, Other comprehensive income before reclassifications
Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity, Amounts reclassified from accumulated other comprehensive income	(229)	(254)	(406)	(512)
Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity, Period change			(406)	(512)
Ending Balance, Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity	1,598	2,449	1,598	2,449
Beginning Balance, Accumulated Other Comprehensive Income			(6,365)	(902)
Other comprehensive income before reclassifications			(11,526)	579
Amounts reclassified from accumulated other comprehensive income	275	(508)	562	(520)
Other comprehensive income			(10,964)	59
Ending Balance, Accumulated Other Comprehensive Income	$ (17,329)	$ (843)	$ (17,329)	$ (843)