Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Consolidated Balance Sheets [Abstract]
Allowance for doubtful accounts, accounts receivable	$ 369	$ 338
Property, plant and equipment, accumulated depreciation	$ 352,843	$ 346,500
Preferred shares, par value	$ 0.10	$ 0.10
Preferred shares, shares authorized	5,000	5,000
Preferred shares, issued
Common shares, par value	$ 0.10	$ 0.10
Common shares, shares authorized	145,000	145,000
Common shares, issued	54,117	53,936
Common shares, outstanding	54,006	53,825
Treasury shares, shares	111	111