Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Tax expense (benefit) on unrealized gain (loss) on derivatives	$ 1	$ (2)	$ 2	$ (23)
Tax expense (benefit) on foreign currency translation adjustment	(7)	0	(9)	0
Tax expense (benefit) on pension and other post-retirement benefits liability adjustment	$ 799	$ (1,185)	$ 1,529	$ (845)