Share Based Awards - Options activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Options Activity Rollforward
Number of Shares Available for Issuance, Beginning Balance	1,859,997
Options Outstanding, Number, Beginning Balance	7,738,496
Number of Shares Available for Issuance, Authorized	4,860,197
Number of Shares Available for Issuance, Granted	(150,000)
Options Outstanding, Shares Granted	150,000
Options exercised	(378,398)
Number of Shares Available for Issuance, Cancelled	646,451
Number of Shares Available for Issuance, Ending Balance	5,909,103	1,859,997
Options Outstanding, Number, Ending Balance	6,863,647	7,738,496
Vested and exercisable- end of the period	6,190,488
Vested and expected to vest - end of the period	6,756,612
Options Activity, Weighted Average Exercise Price Rollforward
Options Outstanding, Weighted-Average Exercise Price, Beginning Balance	$ 4.34
Options Outstanding, Weighted Average Exercise Price Granted	4.75
Options Outstanding, Weighted Average Exercise Price Exercised	1.73
Options Outstanding, Weighted Average Exercise Price Cancelled	3.90
Options Outstanding, Weighted-Average Exercise Price, Ending Balance	4.53	$ 4.34
Options Outstanding, Weighted-Average Exercise Price, Vested and exercisable	4.51
Options Outstanding, Weighted-Average Exercise Price, Vested and expected to vest	$ 4.53
Options Outstanding, Weighted-Average Remaining Contractual Term (Years)	4 years 4 days	3 years 11 months 16 days
Options Outstanding, Weighted-Average Remaining Contractual Term Vested and exercisable (Years)	3 years 7 months 10 days
Options Outstanding, Weighted-Average Remaining Contractual Term Vested and expected to vest (Years)	3 years 11 months 9 days
Options Outstanding, Aggregate Intrinsic Value	$ 7,922	$ 4,897
Options Outstanding, Vested and exercisable, Aggregate Intrinsic Value	7,405
Options Outstanding, Vested and expected to vest, Aggregate Intrinsic Value	$ 7,834
RSUs, excluding Bonus Plans
Options Activity Rollforward
Number of Shares Available for Issuance, other than Options granted	(1,678,750)
Restricted stock units
Options Activity Rollforward
Number of Shares Available for Issuance, other than Options granted	(3,653,521)
Share withheld from net settlement of restricted stock units	(752,564)
Number of Shares Available for Issuance, Restricted stock units cancelled	1,593,415
2017 Bonus Plans
Options Activity Rollforward
Number of Shares Available for Issuance, other than Options granted	(1,974,771)
2017 Bonus Plans | Common Stock
Options Activity Rollforward
Share withheld from net settlement of restricted stock units	(752,564)