Condensed Consolidated Statements of Comprehensive Income (Unaudited) Statement - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 30,754	$ 35,066	$ 87,453	$ 102,967
Other comprehensive income/(loss)
Market value adjustments to marketable securities, net of tax	0	(463)	0	(550)
Market value adjustments on interest rate swap, net of tax	41	365	1,621	(2,673)
Foreign currency translation adjustments	6,078	5,922	22,761	11,232
Supplemental benefit plans adjustments, net of tax	(106)	(107)	1,519	(320)
Total other comprehensive income/(loss)	6,013	5,717	25,901	7,689
Comprehensive income	$ 36,767	$ 40,783	$ 113,354	$ 110,656