Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Plans
Components of net periodic benefit cost:
Interest cost	$ 0		$ 204	$ 0	$ 408
Actuarial loss	0		184	0	369
Settlement charge	0		701	3,325	3,363
Net periodic (income) expense	0		1,089	3,325	4,140
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost	24		98	47	196
Interest cost	52		117	118	233
Expected long-term return on assets	(69)		(114)	(180)	(229)
Prior service cost amortization	(113)		0	(238)	0
Settlement charge	0		0	45	0
Curtailment gain	0	$ (800)	0	(816)	0
Net periodic (income) expense	$ (106)		$ 101	$ (1,024)	$ 200