Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Short term investments amortized cost	$ 163,703	$ 133,744
Stockholders’ equity:
Preferred stock designated Series A, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock designated Series A, shares authorized	10,000,000	10,000,000
Preferred stock designated Series A, shares issued	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	289,865,000	288,923,000
Common stock, shares outstanding	243,714,000	242,829,000
Treasury stock, shares	46,151,000	46,094,000