Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income	$ 12,769	$ 18,612	$ 16,765	$ 27,641
Other comprehensive income (loss):
Foreign currency translation adjustment	1,091	7,753	1,770	10,831
Adjustment to retirement benefit liability, net of tax	(3)	(1)	(6)	(2)
Adjustment to post employment health care benefit liability, net of tax	30	38	59	76
Other comprehensive income	1,118	7,790	1,823	10,905
Total comprehensive income	$ 13,887	$ 26,402	$ 18,588	$ 38,546