Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Customer receivables, allowances	$ 10,348	$ 8,979
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	280,000,000	280,000,000
Common stock, shares outstanding	115,011,172	117,057,696