Benefit Plans - Stock Options Activity Under Share-Based Payment Plans (Details) - Employees and Non Employee Stock Option $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Options
Outstanding as of beginning of period (in shares) | shares	280,457
Granted (in shares) | shares	10,617
Exercised (in shares) | shares	(41,644)
Forfeited, cancelled or expired (in shares) | shares	(1,926)
Outstanding as of end of period (in shares) | shares	247,504
Exercisable (in shares) | shares	115,544
Weighted- Average Exercise Price Per Share
Outstanding as of beginning of period (in dollars per share) | $ / shares	$ 3.76
Granted (in dollars per share) | $ / shares	6.44
Exercised (in dollars per share) | $ / shares	3.18
Forfeited, cancelled or expired (in dollars per share) | $ / shares	4.48
Outstanding as of end of period (in dollars per share) | $ / shares	3.96
Exercisable (in dollars per share) | $ / shares	$ 3.40
Weighted- Average Remaining Contractual Term (Years)
Outstanding	6 years 4 months 24 days
Exercisable	5 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding | $	$ 695,499
Exercisable | $	$ 389,015