Share-Based Awards, Share Option Valuation (Details) - Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands		6 Months Ended		12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	[1]
Stock Option Activity [Roll Forward]
Outstanding at beginning of period (in shares)	[1]	6,959,347
Assumed as part of merger (in shares)		523,456
Granted (in shares)		1,368,378
Exercised (in shares)		61,536
Forfeited (in shares)		(42,713)
Outstanding at end of period (in shares)		8,870,004		6,959,347
Options vested and exercisable at end of period (in shares)		6,476,383
Weighted Average Exercise Price [Abstract]
Outstanding at beginning of period (in dollars per share)	[1]	$ 1.06
Assumed as part of merger (in dollars per share)		2.01
Granted (in dollars per share)		17.63
Exercised (in dollars per share)		0
forfeited (in dollars per share)		1.35
Outstanding at end of period (in dollars per share)		3.90		$ 1.06
Options vested and exercisable at end of period (in dollars per share)		$ 1.17
Weighted-Average Remaining Contractual Term [Abstract]
Outstanding		7 years 11 months 16 days		8 years 2 months 1 day
Assumed as part of merger		7 years 3 months 11 days
Granted		9 years 8 months 19 days
Options vested and exercisable		6 years 10 months 24 days
Aggregate Intrinsic Value [Abstract]
Outstanding		$ 137,631		$ 27,175
Options vested and exercisable		$ 119,582
Employees and Directors [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate		2.60%	2.02%
Expected term		5 years 9 months 11 days	5 years 8 months 26 days
Expected volatility		88.60%	91.90%
Expected dividend yield		0.00%	0.00%
Exercise price (in dollars per share)		$ 17.63	$ 2.14
Fair value of common stock (in dollars per share)		$ 17.63	$ 1.63
Non-Employees [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate		2.74%
Expected term		10 years
Expected volatility		83.79%
Expected dividend yield		0.00%
Exercise price (in dollars per share)		$ 18.75
Fair value of common stock (in dollars per share)		$ 18.75

[1] Affected by Exchange Ratio