Employee Benefit Plans - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 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	2,452,116
Exercised | shares	(2,956,897)
Forfeited | shares	(873,331)
Expired | shares	(917,719)
Outstanding, vested and expected to vest at June 30, 2019 | shares	16,156,544	18,452,375
Vested and exercisable at June 30, 2019 | shares	8,712,991
Weighted Average Exercise Price
Outstanding, vested and expected to vest at December 31, 2018 | $ / shares	$ 14.39
Granted | $ / shares	12.73
Exercised | $ / shares	12.73
Forfeited | $ / shares	14.30
Expired | $ / shares	15.95
Outstanding, vested and expected to vest at June 30, 2019 | $ / shares	14.36	$ 14.39
Vested and exercisable at June 30, 2019 | $ / shares	$ 14.78
Additional Disclosures
Outstanding, vested and expected to vest, Aggregate Intrinsic Value, Beginning balance | $	$ 34,902	$ 8,482
Vested and exercisable at June 30, 2019 | $	$ 15,165
Outstanding, vested and expected to vest, Weighted Average Remaining Contractual Term	7 years 8 months 12 days	7 years 6 months
Vested and exercisable, Weighted Average Remaining Contractual Term	6 years 9 months 18 days