Employee Benefit Plans - Postretirement Healthcare Plan (Details) (Postretirement Healthcare Plan, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Postretirement Healthcare Plan
Defined Benefit Plan Disclosure
Minimum age requirement	55 years
Requisite service period	15 years
Unfunded benefit obligation	$ 4,432	$ 3,948
Net periodic benefit cost	561	507	502
Assumptions used calculating net periodic benefit cost, discount rate	4.30%	4.30%
Assumptions used calculating net periodic benefit cost, rate of compensation increase	5.00%	5.00%
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2013	165
2014	175
2015	163
2016	149
2017	181
2018 through 2022	1,221
Accumulated other comprehensive income (loss), before tax, related to the Plan	2,549
Accumulated other comprehensive income (loss), net of tax	1,546
Net acturarial loss, net of tax	2,137
Unamortized transition asset, net of tax	412
Estimated amount amortized from accumulated other comprehensive loss into net periodic benefit costs	$ 147