Debt - Covenants, Events of Default and Provisions (Details)	9 Months Ended
	Sep. 30, 2018 USD ($)
Debt Instrument [Line Items]
Protection provision, indebtedness yield increase (as a percent)	0.50%
Protection provision, additional loan yield minimum (as a percent)	0.50%
Revolving Credit Facility
Debt Instrument [Line Items]
Minimum incremental facilities	$ 250,000,000
Minimum aggregate restricted payments	$ 50,000,000
Proceed reinvestment period	360 days
Prepayment percentage	75.00%
Prepayment percentage, step-down one	50.00%
Prepayment percentage, step-down two	25.00%
Prepayment percentage, step-down three	0.00%
Current borrowing capacity	$ 468,000,000
Maximum | Revolving Credit Facility
Debt Instrument [Line Items]
First lien net leverage ratio	6.25
Minimum | Revolving Credit Facility
Debt Instrument [Line Items]
First lien net leverage ratio	4.0