Inventory (Schedule of Inventory) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Inventories [Abstract]
Finished goods	$ 65,335us-gaap_InventoryFinishedGoods	$ 55,166us-gaap_InventoryFinishedGoods
Work-in-process	16,188us-gaap_InventoryWorkInProcess	11,332us-gaap_InventoryWorkInProcess
Raw materials	21,855us-gaap_InventoryRawMaterials	19,485us-gaap_InventoryRawMaterials
Total inventories at current costs	103,378us-gaap_InventoryGross	85,983us-gaap_InventoryGross
Less: LIFO reserve	(8,289)us-gaap_InventoryLIFOReserve	(9,027)us-gaap_InventoryLIFOReserve
Inventory	95,089us-gaap_InventoryNet	76,956us-gaap_InventoryNet
Excess of Book LIFO Over Tax LIFO	11,697fstr_ExcessOfBookLifoOverTaxLifoValue	12,241fstr_ExcessOfBookLifoOverTaxLifoValue
Effect Of Inventory Liquidation On Cost Of Good Sold, Increase/(Decrease)	$ 6	$ 1,128	$ 15

Excess amount of book LIFO over tax LIFO at the reporting date.

No definition available.

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- Definition

The effect of liquidating LIFO (last in first out) inventory layers on income.

+ References

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- Definition

Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

+ References

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-Name Regulation S-X (SX)

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- Definition

Gross amount, as of the balance sheet date, of merchandise, goods, commodities, or supplies held for future sale or to be used in manufacturing, servicing or production process.

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Amount of difference between inventory at lower of LIFO cost or market and inventory at lower of other inventory accounting method cost or market, for example, but not limited to, FIFO or average cost.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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- Definition

Amount before valuation and LIFO reserves of raw materials expected to be sold, or consumed within one year or operating cycle, if longer.

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Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer.

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