Consolidated Balance Sheets Parenthetical - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts		$ 4,814	$ 12,504
Preferred stock par value (usd per share)		$ 0.001	$ 0.001
Preferred stock authorized for issuance, shares		40,000,000	40,000,000
Preferred stock, shares issued		0	0
Preferred stock, shares outstanding		0	0
Treasury stock issued, shares		14,102,185	14,102,453
Assets	[1]	$ 8,169,328	$ 9,401,051
Liabilities	[1]	$ 4,952,148	$ 5,855,368
Common Class A
Common stock par value (usd per share)		$ 0.001	$ 0.001
Common stock authorized for issuance, shares		1,000,000,000	1,000,000,000
Common stock issued, shares		101,429,999	100,416,516
Common stock outstanding, shares		87,327,814	86,314,063
Common Class B
Common stock par value (usd per share)		$ 0.001	$ 0.001
Common stock authorized for issuance, shares		1,000,000,000	1,000,000,000
Common stock issued, shares		5,557	5,605
Common stock outstanding, shares		5,557	5,605
Senior Secured Credit Agreement | Term Loan Facility
Debt instrument, unamortized discount and debt issuance costs		$ 24,000	$ 31,000
Current | Senior Secured Credit Agreement | Term Loan Facility
Debt instrument, unamortized discount and debt issuance costs		0	7,917
Noncurrent | Senior Secured Credit Agreement | Term Loan Facility
Debt instrument, unamortized discount and debt issuance costs		36,332	38,830
Variable Interest Entity, Primary Beneficiary
Assets		81,000	97,000
Liabilities		$ 29,000	$ 3,000

[1] The Company’s consolidated total assets as of December 31, 2017 and December 31, 2016 include total assets of variable interest entities (“VIEs”) of $81 million and $97 million, respectively, which can only be used to settle the obligations of the VIEs. The Company’s consolidated total liabilities as of December 31, 2017 and December 31, 2016 include total liabilities of the VIEs of $29 million and $3 million, respectively, for which the creditors of the VIEs have no recourse to the Company (see Note 1).