Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 6,308	$ 5,262
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 89,450	$ 88,422
Equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	128,693,692	128,304,354
Treasury stock, shares held	2,896,627	2,823,191