Description of Business and Basis of Presentation - Schedule of Unaudited Pro forma Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements Captions [Line Items]
Total current assets	$ 99,430		$ 89,146
Total noncurrent assets	58,700
Total assets	158,130		135,417
Total current liabilities	86,846		88,354
Other noncurrent liabilities	10,076		7,304
Total liabilities	96,922		98,907
Temporary equity	367,330		294,200
Stockholder’s equity (deficit)
Common stock	1
Additional paid-in capital	1,729
Accumulated other comprehensive income	5		(25)
Accumulated deficit	(307,857)		(257,665)
Total stockholders’ deficit	(306,122)	$ (280,979)	(257,690)	$ (210,213)	$ (191,611)	$ (176,986)
Total liabilities, redeemable convertible preferred stock, convertible preferred stock and stockholders’ deficit	158,130		135,417
Redeemable Convertible Preferred Stock
Condensed Balance Sheet Statements Captions [Line Items]
Temporary equity	198,228	198,308	151,381	144,910	51,476	50,367
Convertible Preferred Stock
Condensed Balance Sheet Statements Captions [Line Items]
Temporary equity	169,102	$ 169,098	$ 142,819	$ 133,192	$ 122,990	$ 122,990
Pro Forma Adjustments
Condensed Balance Sheet Statements Captions [Line Items]
Total current assets	320,850
Total noncurrent assets	(5,307)
Total assets	315,543
Other noncurrent liabilities	(2,710)
Total liabilities	(2,710)
Stockholder’s equity (deficit)
Common stock	1
Additional paid-in capital	685,582
Total stockholders’ deficit	685,583
Total liabilities, redeemable convertible preferred stock, convertible preferred stock and stockholders’ deficit	315,543
Pro Forma Adjustments | Redeemable Convertible Preferred Stock
Condensed Balance Sheet Statements Captions [Line Items]
Temporary equity	(198,228)
Pro Forma Adjustments | Convertible Preferred Stock
Condensed Balance Sheet Statements Captions [Line Items]
Temporary equity	(169,102)
Pro Forma
Condensed Balance Sheet Statements Captions [Line Items]
Total current assets	420,280
Total noncurrent assets	53,393
Total assets	473,673
Total current liabilities	86,846
Other noncurrent liabilities	7,366
Total liabilities	94,212
Stockholder’s equity (deficit)
Common stock	2
Additional paid-in capital	687,311
Accumulated other comprehensive income	5
Accumulated deficit	(307,857)
Total stockholders’ deficit	379,461
Total liabilities, redeemable convertible preferred stock, convertible preferred stock and stockholders’ deficit	$ 473,673