Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income	$ 13,786	$ 18,612	$ 9,029	$ 13,632	$ 27,641	$ 41,427	$ 23,228
Other comprehensive income (loss):
Foreign currency translation adjustment	(193)			(3,005)		10,638	(4,667)
Reclassification of loss on cash flow hedges, net of tax	0			0		0	143
Adjustment to retirement benefit liability, net of tax	61			3		59	7
Adjustment to post-retirement health care liability, net of tax	38			36		114	110
Other comprehensive (loss) income	(94)			(2,966)		10,811	(4,407)
Total comprehensive income	$ 13,692			$ 10,666		$ 52,238	$ 18,821