Consolidated Statements of Comprehensive (Loss)/Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 9,546	$ 26,729	$ 35,573	$ 91,206
Other comprehensive (loss)/income:
Foreign currency translation adjustments	(13,114)	32	(15,460)	(10,504)
Interest rate swap, net of tax of $267, $0, $2,099 and $0 at respective dates	(685)		(5,380)
Pension plan amortization of net actuarial loss and prior service cost, net of tax of $81, $69, $245 and $246 at respective dates	237	202	717	703
Comprehensive (loss)/income	$ (4,016)	$ 26,963	$ 15,450	$ 81,405