Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 7,511	$ 7,847
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 56,969	$ 44,695
Equity:
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	83,032,028	83,023,628
Treasury stock, shares held	2,771,588	2,766,958