Stock-Based Compensation and Employee Benefit Plan - Stock Option and Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Options/ RSUs Available for Grant
Options/RSUs available for grant, balance (in shares)	1,037,616	2,768,450
Added to plan (in shares)	13,878,793	647,159
Granted (in shares)	(423,854)	(2,698,594)
Cancelled (in shares)	813,078	967,760
Expired (in shares)	(543,306)	(647,159)
Options/RSUs available for grant, balance (in shares)	14,762,327	1,037,616	2,768,450
Outstanding Options/RSUs, Number of Shares
Outstanding (in shares)	14,744,981	13,171,196
Granted (in shares)	423,854	2,698,594
Exercised (in shares)	(219,724)	(157,049)
Cancelled (in shares)	(813,078)	(967,760)
Outstanding (in shares)	14,136,033	14,744,981	13,171,196
Outstanding Options Weighted Average Exercise Price
Outstanding (in dollars per share)	$ 26.42	$ 23.85
Granted (in dollars per share)	27.95	30.96
Exercised (in dollars per share)	3.69	2.76
Cancelled (in dollars per share)	9.32	7.44
Outstanding (in dollars per share)	$ 28.11	$ 26.42	$ 23.85
Outstanding, remaining contractual life	6 years 1 month 28 days	6 years 2 months 9 days	6 years 1 month 10 days
Outstanding, aggregate intrinsic value	$ 31,403	$ 52,703	$ 74,717
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Vested and expected to vest (in shares)	10,917,867
Exercisable (in shares)	7,483,523
Vested and expected to vest, weighted average exercise price (in dollars per share)	$ 28.08
Exercisable, weighted average exercise price (in dollars per share)	$ 26.77
Vested and expected to vest, remaining contractual life	6 years 1 month 17 days
Exercisable, remaining contractual life	5 years 15 days
Vested and expected to vest, aggregate intrinsic value	$ 31,402
Exercisable, aggregate intrinsic value	$ 31,349