CONDENSED CONSOLIDATED BALANCE SHEETS (unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2016	Dec. 31, 2017
Current assets:
Trade accounts receivable, allowance for doubtful accounts	$ 10,172		$ 9,015
Other intangible assets accumulated amortization	$ 89,002		$ 84,624
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)	17,354,300		17,315,573
Series A Preferred Stock [Member]
Equity:
Preferred stock, voting rights	1/10th vote per share	1/10th vote per share
Preferred stock, par value (in dollars per share)	$ 1.00		$ 1.00
Preferred stock, liquidation preference (in dollars per share)	100		100
Preferred stock, stated value (in dollars per share)	$ 112		$ 112
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, voting rights	1/10th vote per share	1/10th vote per share
Preferred stock, par value (in dollars per share)	$ 1.00		$ 1.00
Preferred stock, liquidation preference (in dollars per share)	1,500		1,500
Preferred stock, stated value (in dollars per share)	$ 100		$ 100
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