Retirement Plans and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Employee hire date no longer eligible for noncontributory retirement plan	Dec. 08, 2009
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, non-qualified plans, estimated employer contributions for next fiscal year		$ 160
Defined benefit plan, contributions by employer	$ 40
Defined benefit plan, benefits paid	609
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected employer contributions for next fiscal year		$ 117
Defined benefit plan, contributions by employer	20
Defined benefit plan, benefits paid	$ 20