Condensed Consolidated Statements of Comprehensive Income (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Condensed Consolidated Statements of Comprehensive Income (unaudited) [Abstract]
Net earnings	$ 15,172us-gaap_NetIncomeLoss	$ 8,894us-gaap_NetIncomeLoss
Other comprehensive loss, net of tax:
Net foreign currency translation adjustment	(2,680)	(18)
Net change in postretirement benefit plan, net of taxes of $2 and $1 for the three months ended March 31, 2015 and 2014	(3)	(2)
Other comprehensive loss	(2,683)	(20)
Comprehensive income	$ 12,489us-gaap_ComprehensiveIncomeNetOfTax	$ 8,874us-gaap_ComprehensiveIncomeNetOfTax

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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Amount after tax of (increase) decrease in the value of the projected benefit obligation related to a change in an actuarial assumption and increase (decrease) in the value of the plan assets resulting from experience different from that assumed, that has not been recognized in net periodic benefit (cost) credit.

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Amount after tax and 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 and reclassification adjustments of other comprehensive income (loss).

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