Equity and EPS - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications	$ 173	$ 99	$ (318)
Amounts reclassified from accumulated other comprehensive income	(111)	28	550
Other comprehensive income	62	127	232
Pension Plan Items and Post-Employment Benefit Plan Items | Pension Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	0	0	(244)
Other comprehensive income (loss) before reclassifications	0	0	(355)
Amounts reclassified from accumulated other comprehensive income	0	0	599
Other comprehensive income	0	0	244
Ending Balance	0	0	0
Pension Plan Items and Post-Employment Benefit Plan Items | Postemployment Retirement Benefits
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(376)	(510)	(456)
Other comprehensive income (loss) before reclassifications	181	113	47
Amounts reclassified from accumulated other comprehensive income	(115)	21	(101)
Other comprehensive income	66	134	(54)
Ending Balance	(310)	(376)	(510)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	3	10	(32)
Other comprehensive income (loss) before reclassifications	(8)	(14)	(10)
Amounts reclassified from accumulated other comprehensive income	4	7	52
Other comprehensive income	(4)	(7)	42
Ending Balance	(1)	3	10
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(373)	(500)	(732)
Ending Balance	$ (311)	$ (373)	$ (500)