Net Loss per Share Attributable to Common Stockholders - Schedule of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss attributable to Class A and Class B common stockholders	$ (99,781)	$ (78,579)	$ (45,677)	$ (17,716)	$ (67,761)	$ (71,831)	$ (63,475)	$ (59,532)	$ (241,753)	$ (262,599)	$ (279,658)
Less: noncumulative dividends to preferred stockholders									0	0	0
Less: undistributed earnings to participating securities									0	0	0
Net loss attributable to common stockholders (basic)									(241,753)	(262,599)	(279,658)
Add: adjustments to undistributed earnings to participating securities									0	0	0
Net loss attributable to Class A and Class B common stockholders (diluted)									$ (241,753)	$ (262,599)	$ (279,658)
Denominator:
Weighted average shares of common stock (basic)									53,268	10,248	10,046
Effect of potentially dilutive stock options									0	0	0
Weighted average shares of common stock-diluted (in shares)									53,268	10,248	10,046
Net loss per share attributable to Class A and Class B common stockholders:
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.91)	$ (0.97)	$ (4.34)	$ (1.70)	$ (6.56)	$ (6.97)	$ (6.22)	$ (5.87)	$ (4.54)	$ (25.62)	$ (27.84)