Stockholders' Equity - Option Activities (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Number of Shares Underlying Outstanding Options
Outstanding, beginning balance (in shares)	4,564
Options granted (in shares)	0
Options exercised (in shares)	(504)
Options canceled (in shares)	(21)
Outstanding, ending balance (in shares)	4,039	4,564
Vested and exercisable (in shares)	2,609
Weighted- Average Exercise Price per Share
Outstanding, beginning balance (in dollars per share)	$ 42.50
Options granted (in dollars per share)	0
Options exercised (in dollars per share)	25.36
Options canceled (in dollars per share)	159.36
Outstanding, ending balance (in dollars per share)	44.03	$ 42.50
Vested and exercisable (in dollars per share)	$ 30.93
Weighted- Average Remaining Contractual Term (Years) and Aggregate Intrinsic Value of Stock Options
Weighted-average remaining contractual term of stock options outstanding	4 years	4 years 4 months 24 days
Weighted-average remaining contractual term of stock options vested and exercisable	3 years 7 months 6 days
Aggregate intrinsic value of stock options outstanding	$ 674,925	$ 740,387
Aggregate intrinsic value of stock options outstanding, vested and exercisable	$ 467,293