Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Jan. 27, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Long-term Debt	$ 2,919,185		$ 3,411,551
Term C Loan Facility | Senior Secured Credit Agreement
Related Party Transaction [Line Items]
Long-term Debt	1,644,109	$ 1,761,000	0
Term B Loans Facility | Senior Secured Credit Agreement
Related Party Transaction [Line Items]
Long-term Debt	187,725		2,312,218
Equity Funds | Principal Owner
Related Party Transaction [Line Items]
Fair value of investment in loan fund limited partnership				$ 30,000
Equity Funds | Principal Owner | Term C Loan Facility | Senior Secured Credit Agreement
Related Party Transaction [Line Items]
Long-term Debt	$ 28,000
Equity Funds | Principal Owner | Term B Loans Facility | Senior Secured Credit Agreement
Related Party Transaction [Line Items]
Long-term Debt			$ 31,000
Common Class A
Related Party Transaction [Line Items]
Shares Resold, Per Demand Registration Rights, for Selling Stockholders	7,000,000