Statements of Consolidated Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income Net Of Tax [Abstract]
Net income	$ 9,054	$ 6,278	$ 21,318	$ 11,952
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment	(563)	2,960	(10,098)	11,242
Recognized net actuarial gain (net of tax provision of $35 and $30 for the three months ended September 30, 2018 and 2017, respectively, and net of tax provision of $94 and $119 for the nine months ended September 30, 2018 and 2017, respectively.)	116	50	299	205
Other comprehensive income (loss), net of tax	(447)	3,010	(9,799)	11,447
Comprehensive income	$ 8,607	$ 9,288	$ 11,519	$ 23,399