Balance Sheets (Parenthetical) - $ / shares shares in Thousands	Dec. 31, 2019	Dec. 31, 2018
Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000	10,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	150,000	150,000
Common stock, shares issued	33,739	33,341
Common stock, shares outstanding	33,739	33,341