Comprehensive Income - Components of Accumulated Other Comprehensive Income (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
Statement Of Income And Comprehensive Income [Abstract]
Beginning Balance, Defined Benefit Pension Plan			$ (7,966)	$ (21,401)
Defined Benefit Pension Plan, Other comprehensive income before reclassifications
Defined Benefit Pension Plan, Amounts reclassified from accumulated other comprehensive income	239	575	475	1,050
Defined Benefit Pension Plan, Period change			475	1,050
Ending Balance, Defined Benefit Pension Plan	(7,491)	(20,351)	(7,491)	(20,351)
Beginning Balance, Unrealized Gains (Losses) on Securities Available-for-Sale			(6,126)	13,032
Unrealized Gains (Losses) on Securities Available-for-Sale, Other comprehensive income before reclassifications			7,194	(11,526)
Unrealized Gains (Losses) on Securities Available-for-Sale, Amounts reclassified from accumulated other comprehensive income	(107)	(71)	(157)	(82)
Net effect on other comprehensive income for the period			7,037	(11,608)
Ending Balance, Unrealized Gains (Losses) on Securities Available-for-Sale	911	1,424	911	1,424
Beginning Balance, Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity			1,358	2,004
Unrealized Gains 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	(84)	(229)	(171)	(406)
Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity, Period change			(171)	(406)
Ending Balance, Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity	1,187	1,598	1,187	1,598
Beginning Balance, Accumulated Other Comprehensive Income			(12,734)	(6,365)
Other comprehensive income before reclassifications			7,194	(11,526)
Amounts reclassified from accumulated other comprehensive income	48	275	147	562
Other comprehensive income			7,341	(10,964)
Ending Balance, Accumulated Other Comprehensive Income	$ (5,393)	$ (17,329)	$ (5,393)	$ (17,329)