Condensed Consolidated Balance Sheets (Parenthetical) - Unaudited (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Condensed Consolidated Balance Sheets [Abstract]
Allowance for Accounts receivable	$ 747	$ 811
Accumulated depreciation	$ 235,382	$ 240,693
Preferred stock, without par value
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued
Common stock, without par value
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	55,495,710	55,263,082
Common stock held in treasury, shares	21,935,218	21,829,954