Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Components of accumulated other comprehensive income
Beginning Balance, Defined Benefit Pension Plan	$ (21,401)	$ (15,155)
Beginning balance, Unrealized Gains (Losses) on Securities Available-for-Sale	13,032	11,292
Beginning balance, Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity	2,004	2,961
Beginning balance, Accumulated other comprehensive income	(6,365)	(902)
Defined Benefit Pension Plan, Other comprehensive income before reclassifications
Unrealized Gains (Losses) on Securities Available-for-Sale, Other comprehensive income before reclassifications	(729)	588
Unrealized Gains (Losses) on Securities Transferred from Available-for-Sale to Held-to-maturity, other comprehensive income before reclassifications
Other comprehensive income before reclassifications	(729)	588
Defined Benefit Pension Plan, Amounts reclassified from accumulated other comprehensive income	475	309
Unrealized Gains (Losses) on Securities Available-for-Sale, Amounts reclassified from accumulated other comprehensive income	(10)	(63)
Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity, Amounts reclassified from accumulated other comprehensive income	(177)	(258)
Amounts reclassified from accumulated other comprehensive income	288	(12)
Defined Benefit Pension Plan, Period change	475	309
Unrealized Gains (Losses) on Securities Available-for-Sale, Period change	(739)	525
Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity, Period change	(177)	(258)
Other comprehensive income	(441)	576
Ending Balance, Defined Benefit Pension Plan	(20,926)	(14,846)
Ending balance, Unrealized Gains (Losses) on Securities Available-for-Sale	12,293	11,817
Ending balance, Unrealized Gains on Securities Transferred from Available-for-Sale to Held-to-Maturity	1,827	2,703
Ending balance, Accumulated other comprehensive income	$ (6,806)	$ (326)