Stock Incentive Plans - Summary of Option Activity under Plans (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding at Beginning Balance	1,971,711
Number of Options, Granted	755,507
Number of Options, Exercised	(26,204)	0
Number of Options, Cancelled/Forfeited	(16,609)
Number of Options, Outstanding at Ending Balance	2,684,405	1,971,711
Number of Options, Exercisable at March 31, 2018	216,985
Number of Options, Vested and expected to vest at March 31, 2018	2,684,405
Weighted-Average Exercise Price per Share, Outstanding at Beginning Balance	$ 3.61
Weighted-Average Exercise Price per Share, Granted	15.71
Weighted-Average Exercise Price per Share, Exercised	2.64
Weighted-Average Exercise Price per Share, Cancelled/Forfeited	1.28
Weighted-Average Exercise Price per Share, Outstanding at Ending Balance	7.03	$ 3.61
Weighted-Average Exercise Price per Share, Exercisable at March 31, 2018	0.41
Weighted-Average Exercise Price per Share, Vested and expected to vest at March 31, 2018	$ 7.03
Weighted Average Remaining Contractual Term, Outstanding	9 years 3 months 18 days	9 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable at March 31, 2018	8 years
Weighted Average Remaining Contractual Term, Vested and expected to vest at March 31, 2018	9 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding Ending Balance	$ 31,329,115	$ 5,977,162
Aggregate Intrinsic Value, Exercisable at March 31, 2018	3,969,527
Aggregate Intrinsic Value, Vested and expected to vest at March 31, 2018	$ 31,329,115