Other Comprehensive Loss - Related Tax Effects Allocated to Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Retirement benefits adjustment, before tax amount	$ (763)	$ (893)	$ (2,481)	$ (2,478)
Cumulative translation adjustment, before tax amount	1,130	621	5,209	215
Total other comprehensive income (loss), before tax amount	367	(272)	2,728	(2,263)
Retirement benefits adjustment, tax	217	228	651	779
Cumulative translation adjustment, tax	0	0	0	0
Total other comprehensive income (loss), tax	217	228	651	779
Retirement benefits adjustment, after tax amount	(546)	(665)	(1,830)	(1,699)
Cumulative translation adjustment, after tax amount	1,130	621	5,209	215
Total other comprehensive income (loss)	$ 584	$ (44)	$ 3,379	$ (1,484)