Long-term Debt - Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Debt	$ 303,080	$ 374,650
Credit Agreement [Member]
Debt Instrument [Line Items]
Debt	10,810	333,720
Senior Notes [Member]
Debt Instrument [Line Items]
Debt	300,000	0
Revolving Credit Facility [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Debt	10,810	75,910
Senior Secured Term Loan A [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Debt	0	257,810
Fair Value, Inputs, Level 2 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Fair Value	300,750	0
Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term Debt, Fair Value	10,490	75,380
Fair Value, Inputs, Level 2 [Member] | Senior Secured Term Loan A [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term Debt, Fair Value	$ 0	$ 256,780