Share-Based Compensation - Summary of Equity Awards Authorized and Available for Future Grant (Details)	6 Months Ended
	Jun. 30, 2018 shares
2018 Plan
Available for future grants
Available for future grants at beginning of period (in shares)	0
Newly authorized shares (in shares)	3,800,000
Granted (in shares)	(925)
Cancellation and forfeitures (in shares)	0
Plan termination (in shares)	0
Available for future grants at end of period (in shares)	3,799,075
2015 Plan
Available for future grants
Available for future grants at beginning of period (in shares)	1,437,435
Newly authorized shares (in shares)	0
Granted (in shares)	(360,999)
Cancellation and forfeitures (in shares)	0
Plan termination (in shares)	(1,076,436)
Available for future grants at end of period (in shares)	0