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Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income	$ 13,117	$ 19,503	$ 22,837	$ 8,352	$ 25,176	$ 20,619	$ 12,769	$ 3,996	$ 63,809	$ 62,560	$ 33,675
Other comprehensive (loss) income:
Foreign currency translation adjustment									(3,241)	3,150	6,945
Cumulative effect of accounting change (see Note 1)									(350)	0	0
Adjustment to pension and post-retirement benefit liability, net of tax									723	205	750
Other comprehensive (loss) income									(2,868)	3,355	7,695
Total comprehensive income									$ 60,941	$ 65,915	$ 41,370

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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