Accumulated Other Comprehensive (Loss) Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (11,240)		$ (11,734)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	44	1,058
Pension and postretirement benefits	450	342
Total other comprehensive income adjustments	494	1,400
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	44	44	0	(1,014)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	44	1,058
Pension and postretirement benefits	0	0
Total other comprehensive income adjustments	44	1,058
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(11,284)	(9,645)	(11,734)	(9,987)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	0	0
Pension and postretirement benefits	450	342
Total other comprehensive income adjustments	450	342
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(11,240)	(9,601)	(11,734)	(11,001)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax	44	1,058
Pension and postretirement benefits	450	342
Total other comprehensive income adjustments	$ 494	$ 1,400