CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Trade accounts receivable, allowance for doubtful accounts (in dollars)	$ 3,986	$ 4,379
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	40,835,651	40,298,852
Common stock, shares outstanding	36,680,469	34,991,629
Treasury stock, shares	4,155,182	5,307,223
Participating preferred stock
Preferred stock, par value (in dollars per share)	$ 1	$ 0
Preferred stock, shares authorized	100,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0