Long-Term Debt - Interest, Fees, and Principal Payments (Details) - USD ($) $ in Millions						9 Months Ended
	Oct. 06, 2017	Nov. 08, 2016	Oct. 13, 2016	May 09, 2016	Nov. 20, 2013	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2015
Prior Senior Secured Credit Facility, Term Loan Facility
Long-Term Debt
Repayments of debt			$ 200.4
Secured Debt | Line of Credit | Interest on Debt Instrument, Option One | London Interbank Offered Rate (LIBOR)
Long-Term Debt
Variable rate spread (as a percent)	3.00%					3.75%
Secured Debt | Line of Credit | Interest on Debt Instrument, Option Two
Long-Term Debt
Variable rate spread (as a percent)	2.00%					2.75%
Secured Debt | Line of Credit | Prior Senior Secured Credit Facility, Term Loan Facility
Long-Term Debt
Quarterly scheduled principal payment					$ 8.9
Prepayment requirement as a percentage of excess cash flow (as a percent)					50.00%
Prepayment requirement as a percentage of excess cash flow, reduced amount (as a percent)					25.00%
Excess cash flow offer							$ 0.0	$ 16.1
Principal prepayment offered and paid				$ 12.0
Secured Debt | Line of Credit | Prior Senior Secured Credit Facility, Term Loan Facility | Minimum
Long-Term Debt
Prepayment requirement as a percentage of excess cash flow, reduced amount, leverage ratio					2.00
Secured Debt | Line of Credit | Prior Senior Secured Credit Facility, Term Loan Facility | Maximum
Long-Term Debt
Prepayment requirement as a percentage of excess cash flow, reduced amount, leverage ratio					2.50
Secured Debt | Line of Credit | Prior Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option One | London Interbank Offered Rate (LIBOR)
Long-Term Debt
Variable rate basis floor (as a percent)					1.00%
Variable rate spread (as a percent)					4.75%
Secured Debt | Line of Credit | Prior Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option Two
Long-Term Debt
Alternate base rate (as a percent)					3.75%
Base rate spread (as a percent)					2.00%
Secured Debt | Line of Credit | Prior Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option Two | Federal Funds Effective Rate
Long-Term Debt
Variable rate spread (as a percent)					0.50%
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility
Long-Term Debt
Prepayment requirement as a percentage of excess cash flow (as a percent)							50.00%
Prepayment requirement as a percentage of excess cash flow, reduced amount (as a percent)							25.00%
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility | Minimum
Long-Term Debt
Prepayment requirement as a percentage of excess cash flow, reduced amount, leverage ratio							1.50
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility | Maximum
Long-Term Debt
Prepayment requirement as a percentage of excess cash flow, reduced amount, leverage ratio							2.00
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option One | London Interbank Offered Rate (LIBOR)
Long-Term Debt
Variable rate basis floor (as a percent)		0.75%
Variable rate spread (as a percent)		3.00%
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option Two
Long-Term Debt
Alternate base rate (as a percent)		2.00%
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option Two | One Month Adjusted London Interbank Offer Rate
Long-Term Debt
Variable rate basis floor (as a percent)		1.75%
Variable rate spread (as a percent)		1.00%
Secured Debt | Line of Credit | Existing Senior Secured Credit Facility, Term Loan Facility | Interest on Debt Instrument, Option Two | Federal Funds Effective Rate
Long-Term Debt
Variable rate spread (as a percent)		0.50%
Secured Debt | Revolving Credit Facility
Long-Term Debt
Commitment fee (as a percent)		0.50%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility
Long-Term Debt
Commitment fee (as a percent)					0.50%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option One
Long-Term Debt
Variable rate basis floor (as a percent)					1.00%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option One | Minimum
Long-Term Debt
Alternate base rate (as a percent)					4.25%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option One | Maximum
Long-Term Debt
Alternate base rate (as a percent)					4.50%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two
Long-Term Debt
Base rate spread (as a percent)					2.00%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | Minimum
Long-Term Debt
Alternate base rate (as a percent)					3.25%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | Maximum
Long-Term Debt
Alternate base rate (as a percent)					3.50%
Secured Debt | Revolving Credit Facility | Prior Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | Federal Funds Effective Rate
Long-Term Debt
Variable rate spread (as a percent)					0.50%
Secured Debt | Revolving Credit Facility | Existing Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option One
Long-Term Debt
Variable rate basis floor (as a percent)		0.75%
Secured Debt | Revolving Credit Facility | Existing Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | Minimum
Long-Term Debt
Variable rate spread (as a percent)		2.25%
Alternate base rate (as a percent)		3.25%
Secured Debt | Revolving Credit Facility | Existing Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | Maximum
Long-Term Debt
Variable rate spread (as a percent)		2.50%
Alternate base rate (as a percent)		3.50%
Secured Debt | Revolving Credit Facility | Existing Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | One Month Adjusted London Interbank Offer Rate
Long-Term Debt
Variable rate spread (as a percent)		1.00%
Secured Debt | Revolving Credit Facility | Existing Senior Secured Credit Facility, Revolving Credit Facility | Interest on Debt Instrument, Option Two | Federal Funds Effective Rate
Long-Term Debt
Variable rate spread (as a percent)		0.50%