Stockholders' Equity and Employee Benefit Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended				19 Months Ended
	Feb. 28, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 31, 2015
Number of Shares
Outstanding, vested and expected to vest, Beginning balance		13,809,069	12,028,622	13,039,688
Granted	2,225,766	5,735,643	4,139,372	5,014,600		16,700,000
Exercised		(81,849)	(35,352)	(45,444)
Forfeited		(832,591)	(1,623,057)	(5,500,606)
Expired		(177,897)	(700,516)	(479,616)
Outstanding, vested and expected to vest, Ending balance		18,452,375	13,809,069	12,028,622	13,039,688
Exercisable at December 31, 2018		10,435,039
Weighted Average Exercise Price
Outstanding, vested and expected to vest, Beginning balance		$ 14.82	$ 14.53	$ 14.39
Granted		13.31	16.03	16.03		$ 42.33
Exercised		6.01	4.35	4.42
Forfeited		15.01	16.02	15.99
Expired		14.08	14.77	10.72
Outstanding, vested and expected to vest, Ending balance		14.39	$ 14.82	$ 14.53	$ 14.39
Exercisable at December 31, 2018		$ 14.31
Additional Disclosures
Outstanding, vested and expected to vest, Aggregate Intrinsic Value, Beginning balance		$ 8,482	$ 9,292	$ 9,903	$ 11,142
Exercisable, Aggregate Intrinsic Value at September 30, 2018		$ 8,436
Outstanding, vested and expected to vest, Weighted Average Remaining Contractual Term		7 years 6 months	7 years 9 months 18 days	8 years 3 months 18 days	8 years 9 months 18 days
Exercisable, Weighted Average Remaining Contractual Term		6 years 7 months 6 days