Net Loss per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net loss	$ 15,372	$ (2,056)	$ (118,268)	$ (80,877)	$ (45,470)	$ (113,403)	$ (58,240)	$ (60,079)	$ (185,829)	$ (277,192)	$ (102,777)
Denominator:
Weighted-average shares of common stock— basic for Class A and Class B (in shares)									244,603	232,032	220,405
Effect of dilutive securities (in shares)									0	0	0
Weighted-average shares of common stock—diluted for Class A and Class B (in shares)									244,603	232,032	220,405
Net loss per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.06	$ (0.01)	$ (0.49)	$ (0.34)	$ (0.19)	$ (0.48)	$ (0.25)	$ (0.27)	$ (0.76)	$ (1.19)	$ (0.47)
Diluted (in dollars per share)	$ 0.06	$ (0.01)	$ (0.49)	$ (0.34)	$ (0.19)	$ (0.48)	$ (0.25)	$ (0.27)	$ (0.76)	$ (1.19)	$ (0.47)