Employee Benefit Plans - Postretirement Healthcare Plan (Details) (Postretirement Healthcare Plan, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Postretirement Healthcare Plan
Defined Benefit Plan Disclosure
Minimum age requirement	55 years
Requisite service period	15 years
Unfunded benefit obligation	$ 3,577	$ 4,870
Net periodic benefit cost	400	571	561
Assumptions used calculating net periodic benefit cost, discount rate	3.60%	4.30%
Assumptions used calculating net periodic benefit cost, rate of compensation increase	5.50%	5.00%
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2015	158
2016	163
2017	194
2018	219
2019	254
2020 through 2024	1,496
Accumulated other comprehensive income (loss), before tax, related to the Plan	613
Accumulated other comprehensive income (loss), net of tax	413
Net acturarial loss, net of tax	257
Unamortized transition asset, net of tax	356
Estimated amount amortized from accumulated other comprehensive loss into net periodic benefit costs	$ 35