Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net income	$ 20,216	$ 15,080
Other comprehensive income:
Foreign currency translation adjustments	1,712	2,030
Change in unrecognized pension benefit cost	65	0
Other comprehensive income	1,777	2,030
Comprehensive income	21,993	17,110
Comprehensive income (loss) attributable to non-controlling interest	(48)	8
Comprehensive income attributable to controlling interest	$ 22,041	$ 17,102

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

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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. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount before tax, after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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