Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Plans
Components of net periodic benefit cost:
Interest cost	$ 0	$ 204
Actuarial loss	0	184
Settlement charge	3,325	2,662
Net periodic (income) expense	3,325	3,050
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost	23	98
Interest cost	66	117
Expected long-term return on assets	(111)	(114)
Prior service cost amortization	(125)	0
Settlement charge	45	0
Curtailment gain	(816)	0
Net periodic (income) expense	$ (918)	$ 101