Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets:
Allowance for doubtful accounts	$ 2,497	$ 2,718
Accumulated depreciation	119,665	121,560
Accumulated amortization	$ 12,924	$ 10,984
Shareholders' Equity:
Preferred stock, shares authorized	500	500
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	70,000	70,000
Common stock, shares issued	38,567	38,478
Common stock, shares outstanding	38,567	38,478
Common stock, no par value	$ 0	$ 0