Debt (Credit Facilities Amendments) (Details) - USD ($)		3 Months Ended				12 Months Ended
	Apr. 19, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2016	Nov. 01, 2017	Oct. 01, 2017	Aug. 31, 2017
Line Of Credit Facility [Line Items]
Deferred financing costs						$ 2,021,000
Credit Facilities Amendments
Line Of Credit Facility [Line Items]
Deferred financing costs						2,000,000
First Lien Facility Amendment | Revolving Credit Facility Conforming Tranche
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity						410,000,000
First Lien Facility Amendment | Revolving Credit Facility Nonconforming Tranche
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity						$ 30,000,000
First Lien Facility Amendment | Scenario, Forecast
Line Of Credit Facility [Line Items]
Lenders’ waivers description	The First Lien lenders’ waivers are subject to revocation in certain circumstances, including the exercise of remedies by junior lenders (including pursuant to our second lien credit facility), the failure to extend the standstill period under the intercreditor agreement at least 15 business days prior to its expiration, and the occurrence of additional events of default under the First Lien Facility.
First Lien Facility Amendment | Scenario, Forecast | Revolving Credit Facility Conforming Tranche
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity								$ 190,000,000	$ 330,000,000
First Lien Facility Amendment | Scenario, Forecast | Revolving Credit Facility Nonconforming Tranche
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity							$ 10,000,000
First Lien Facility Amendment | Scenario, Forecast | Maximum
Line Of Credit Facility [Line Items]
Total Debt to EBITDA		550.00%	550.00%	550.00%	550.00%
Ratio of First Lien Debt to EBITDA		400.00%	400.00%	400.00%	400.00%
First Lien Facility Amendment | After December 31, 2018 (Thereafter) | Maximum
Line Of Credit Facility [Line Items]
Total Debt to EBITDA						500.00%
Ratio of First Lien Debt to EBITDA						350.00%
Current Liability | Credit Facilities Amendments
Line Of Credit Facility [Line Items]
Outstanding indebtedness						$ 666,800,000
Current Liability | Credit Facilities Amendments | Due on May 1, 2017
Line Of Credit Facility [Line Items]
Outstanding indebtedness						30,000,000
Current Portion of Long Term Debt, Net | Credit Facilities Amendments
Line Of Credit Facility [Line Items]
Outstanding indebtedness						$ 694,800,000