Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 15,618	$ 40,419	$ 26,027	$ 64,477
Other comprehensive income/(loss):
Foreign currency translation adjustments	2,432	(13,465)	(2,346)	(10,536)
Interest rate swap, net of tax of $1,053, $0, $1,832 and $0 at respective dates	(2,699)		(4,695)
Pension plan amortization of net actuarial loss and prior service cost, net of tax of $82, $69, $164 and $177 at respective dates	239	206	480	501
Comprehensive income	$ 15,590	$ 27,160	$ 19,466	$ 54,442