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Basis of Presentation and Significant Accounting Policies - (Details Textual) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Service_Center	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Line Items]
Undistributed Earnings of Foreign Subsidiaries	$ 48,585
Service centers	47cas_NumberOfServiceCenters
Joint venture ownership percentage	50.00%
maximum maturity of investments to be considered cash equivalent	90 days
Shipping, Handling and Transportation Costs	35,471	35,171	36,585
Percentage of LIFO inventory	68.00%us-gaap_PercentageOfLIFOInventory	80.00%us-gaap_PercentageOfLIFOInventory
Amount current replacement cost of inventory costs exceeds book value	129,779	130,854
Effect of LIFO Inventory Liquidation on Income		$ 1,834
Percentage tax benefit recognized on dividends declared, joint venture subsidiaries	80.00%
Outstanding common stock equivalents	0	0	0
Number of customers, annual sales in excess of 3% of total annual sales	0
Weighted average forfeiture rate	49.00%cas_WeightedAverageForfeitureRate
Measurement period for targeted goals under the long-term compensation plan	3 years
Stock Options
Accounting Policies [Line Items]
Number of trading days preceeding grant date from which closing stock price used to determine exercise price, 2010 grants, alternate valuation method	10 days
Restricted Stock Units (RSUs)
Accounting Policies [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Non-compete agreements
Accounting Policies [Line Items]
Intangible assets useful lives	3 years
Developed technology
Accounting Policies [Line Items]
Intangible assets useful lives	3 years
Minimum \| Stock Options
Accounting Policies [Line Items]
Contractual period for options granted	8 years
Minimum \| Customer relationships
Accounting Policies [Line Items]
Intangible assets useful lives	4 years
Minimum \| Trade name
Accounting Policies [Line Items]
Intangible assets useful lives	1 year
Maximum
Accounting Policies [Line Items]
Sales Revenue Not Recognized at Shipment, As a Percentage of Total Sales	2.00%	2.00%	2.00%
Maximum \| Stock Options
Accounting Policies [Line Items]
Contractual period for options granted	10 years
Maximum \| Customer Concentration Risk [Member]
Accounting Policies [Line Items]
Percentage concentration of sales	3.00%
Maximum \| Customer relationships
Accounting Policies [Line Items]
Intangible assets useful lives	12 years
Maximum \| Trade name
Accounting Policies [Line Items]
Intangible assets useful lives	10 years
North America
Accounting Policies [Line Items]
Service centers	42
Europe
Accounting Policies [Line Items]
Service centers	3
Asia
Accounting Policies [Line Items]
Service centers	2
United States \| Geographic Concentration Risk
Accounting Policies [Line Items]
Percentage concentration of sales	75.00%
Executives and Employees \| Minimum \| Stock Options and Restricted Stock
Accounting Policies [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	2 years
Executives and Employees \| Maximum \| Stock Options and Restricted Stock
Accounting Policies [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Director \| Stock Options and Restricted Stock
Accounting Policies [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years