Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Short term investments amortized cost	$ 58,139
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	287,093,000	286,877,000
Common stock, shares outstanding	241,016,000	240,805,000
Treasury stock, shares	46,077,000	46,072,000