Other Comprehensive Loss - Related Tax Effects Allocated to Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity [Abstract]
Retirement benefits adjustment, before tax amount	$ (761)	$ (1,418)	$ (1,718)	$ (1,585)
Cumulative translation adjustment, before tax amount	2,256	(713)	4,078	(408)
Total other comprehensive income (loss), before tax amount	1,495	(2,131)	2,360	(1,993)
Retirement benefits adjustment, tax	217	275	434	551
Cumulative translation adjustment, tax	0	0	0	0
Total other comprehensive income (loss), tax	217	275	434	551
Retirement benefits adjustment, after tax amount	(544)	(1,143)	(1,284)	(1,034)
Cumulative translation adjustment, after tax amount	2,256	(713)	4,078	(408)
Total other comprehensive income (loss)	$ 1,712	$ (1,856)	$ 2,794	$ (1,442)