Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Net Unrealized Gain on Available for Sale Securities	Jun. 30, 2012 Net Unrealized Gain on Available for Sale Securities	Jun. 30, 2013 Net Unrealized Gain on Available for Sale Securities	Jun. 30, 2012 Net Unrealized Gain on Available for Sale Securities	Jun. 30, 2013 Defined Benefit Plan	Mar. 31, 2013 Defined Benefit Plan	Dec. 31, 2012 Defined Benefit Plan	Jun. 30, 2012 Defined Benefit Plan	Mar. 31, 2012 Defined Benefit Plan	Dec. 31, 2011 Defined Benefit Plan
Changes in accumulated other comprehensive income by component
Balance at the beginning of the period	$ 3,709	$ 1,699	$ 5,357	$ (1,219)	$ 8,516	$ 5,832	$ 10,164	$ 2,914	$ (4,807)	$ (4,807)	$ (4,807)	$ (4,133)	$ (4,133)	$ (4,133)
Other comprehensive (loss) income before reclassifications	(7,389)	1,338	(8,386)	4,645	(7,389)	1,338	(8,386)	4,645
Amounts reclassified from accumulated other comprehensive (loss) income	(841)	(112)	(1,492)	(501)	(841)	(112)	(1,492)	(501)
Total other comprehensive (loss) income	(8,230)	1,226	(9,878)	4,144	(8,230)	1,226	(9,878)	4,144
Balance at the end of the period	$ (4,521)	$ 2,925	$ (4,521)	$ 2,925	$ 286	$ 7,058	$ 286	$ 7,058	$ (4,807)	$ (4,807)	$ (4,807)	$ (4,133)	$ (4,133)	$ (4,133)