Employee Benefit Plans - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Number of Shares
Outstanding, vested and expected to vest at December 31, 2018 | shares	18,452,375
Granted | shares	3,128,591
Exercised | shares	(3,319,196)
Forfeited | shares	(1,240,835)
Expired | shares	(934,413)
Outstanding, vested and expected to vest at September 30, 2019 | shares	16,086,522	18,452,375
Vested and exercisable at September 30, 2019 | shares	9,412,266
Weighted Average Exercise Price
Outstanding, vested and expected to vest at December 31, 2018 | $ / shares	$ 14.39
Granted | $ / shares	13.95
Exercised | $ / shares	12.65
Forfeited | $ / shares	14.05
Expired | $ / shares	15.88
Outstanding, vested and expected to vest at September 30, 2019 | $ / shares	14.60	$ 14.39
Vested and exercisable at September 30, 2019 | $ / shares	$ 14.86
Additional Disclosures
Outstanding, vested and expected to vest, Aggregate Intrinsic Value, Beginning balance | $	$ 41,101	$ 8,482
Vested and exercisable at September 30, 2019 | $	$ 21,157
Outstanding, vested and expected to vest, Weighted Average Remaining Contractual Term	7 years 6 months	7 years 6 months
Vested and exercisable, Weighted Average Remaining Contractual Term	6 years 7 months 6 days