Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Cash and cash equivalents	$ 392,348	$ 320,567
Current assets	1,454,487	1,288,694
Assets	6,990,536	7,391,285
Current liabilities	1,537,265	1,374,589
Liabilities	$ 5,006,198	$ 5,390,006
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	49,889,000	49,488,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Series A Convertible Redeemable Preferred Stock
Convertible redeemable preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible redeemable preferred stock, shares authorized (in shares)	111,000	512,000
Convertible redeemable preferred stock, shares issued (in shares)	0	401,000
Convertible redeemable preferred stock, shares outstanding (in shares)	0	401,000
Class A Common Stock
Common stock, par value (in dollars per share)	$ 0.004	$ 0.004
Common stock, shares authorized (in shares)	700,000,000	700,000,000
Common stock, shares issued (in shares)	91,654,000	55,052,000
Common stock, shares outstanding (in shares)	91,654,000	55,052,000
Class B Common Stock
Common stock, par value (in dollars per share)	$ 0.004	$ 0.004
Common stock, shares authorized (in shares)	175,000,000	175,000,000
Common stock, shares issued (in shares)	132,387,000	132,443,000
Common stock, shares outstanding (in shares)	132,387,000	132,443,000
Variable Interest Entity, Primary Beneficiary
Cash and cash equivalents	$ 146,927	$ 100,971
Current assets	642,133	407,315
Assets	1,334,870	1,419,579
Current liabilities	314,860	341,147
Liabilities	$ 382,380	$ 449,561