Stock Options, Restricted Stock Units and Employee Stock Purchase Plan - Summary of Unvested PSU Activity (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Performance Shares
Total Number of Units (in thousands)
Unvested at beginning balance (in Shares) | shares	0
Granted (in Shares) | shares	1,239
Vested (in Shares) | shares	0
Forfeited (in Shares) | shares	0
Unvested at ending balance (in Shares) | shares	1,239
Weighted Average Grant Date Fair Value per Unit
Unvested at beginning balance (in Dollars per share) | $ / shares	$ 0
Granted (in Dollars per share) | $ / shares	3.99
Vested (in Dollars per share) | $ / shares	0
Forfeited (in Dollars per share) | $ / shares	0
Unvested at ending balance (in Dollars per share) | $ / shares	$ 3.99
Performance Shares, Vesting Subject to Performance Conditions
Total Number of Units (in thousands)
Unvested at beginning balance (in Shares) | shares	0
Granted (in Shares) | shares	985
Vested (in Shares) | shares	0
Forfeited (in Shares) | shares	0
Unvested at ending balance (in Shares) | shares	985
Weighted Average Grant Date Fair Value per Unit
Unvested at beginning balance (in Dollars per share) | $ / shares	$ 0
Granted (in Dollars per share) | $ / shares	4.06
Vested (in Dollars per share) | $ / shares	0
Forfeited (in Dollars per share) | $ / shares	0
Unvested at ending balance (in Dollars per share) | $ / shares	$ 4.06
Performance Shares, Vesting Subject to Market Conditions
Total Number of Units (in thousands)
Unvested at beginning balance (in Shares) | shares	0
Granted (in Shares) | shares	254
Vested (in Shares) | shares	0
Forfeited (in Shares) | shares	0
Unvested at ending balance (in Shares) | shares	254
Weighted Average Grant Date Fair Value per Unit
Unvested at beginning balance (in Dollars per share) | $ / shares	$ 0
Granted (in Dollars per share) | $ / shares	3.73
Vested (in Dollars per share) | $ / shares	0
Forfeited (in Dollars per share) | $ / shares	0
Unvested at ending balance (in Dollars per share) | $ / shares	$ 3.73