Earnings Per Share - Schedule of Potentially Issuable Common Shares not Included in Computation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock instruments outstanding (shares)	9,190	8,100
Shares issuable upon the release of restricted stock awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock instruments outstanding (shares)	30	16
Shares issuable upon exercise of stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock instruments outstanding (shares)	9,160	8,084