CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Trade accounts receivable, allowance for doubtful accounts	$ 11,037	$ 9,015
Equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock shares issued (in shares)	17,567,912	17,315,573
Series A Preferred Stock [Member]
Equity:
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	1,122	1,122
Preferred stock, outstanding (in shares)	1,122	1,122
Series B Convertible Preferred Stock [Member]
Equity:
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	15,000	15,000
Preferred stock, outstanding (in shares)	15,000	15,000