Employee Benefit Plans - Changes in Plan Assets and Benefit Obligations in Other Comprehensive Income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial (loss) gain			$ (35)
Settlement losses			414
Recognized net actuarial loss			25
Amortization of prior service cost			0
Total other comprehensive income (loss), pre-tax			404
Income tax expense (benefit)	$ 0	$ 0	160
Total other comprehensive income (loss), net of tax	0	0	244
Post-employment benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial (loss) gain	261	293	(35)
Settlement losses	0	0	0
Recognized net actuarial loss	184	269	278
Amortization of prior service cost	(339)	(338)	(338)
Total other comprehensive income (loss), pre-tax	106	224	(95)
Income tax expense (benefit)	40	90	(41)
Total other comprehensive income (loss), net of tax	$ 66	$ 134	$ (54)