Senior Debt (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Senior Debt (Table Details) [Abstract]
Unamortized Debt Issuance Expense	$ 3,100,000				$ 3,100,000		$ 5,200,000
Mandatory Excess Cash Flow Pre-Payment		$ 6,000,000		$ 141,000,000
Line of credit commitment fee					$ 1,100,000
Line of credit commitment fee percentage					0.50%
Senior credit facilities, additional amount allowed	100,000,000				$ 100,000,000
Debt refinancing charges	0		$ 1,936,000		0	$ 1,936,000
Debt arrangement and amendment fees			$ 5,300,000
Letters of credit, amount outstanding	$ 94,000,000				$ 94,000,000
Financial Covenants Ratios (Table Details) [Abstract]
Required consolidated fixed charge coverage ratio, minimum	1.10				1.10
Actual consolidated fixed charge coverage ratio	1.15				1.15
Covenants [Abstract]
Adjusted consolidated EBITDA					$ 53,700,000
Consolidated fixed charges					$ 46,600,000
Event of default-3rd party ownership % of our voting stock	35.00%				35.00%
Event of default-not satisfied or bonded judgment in excess of	$ 50,000,000				$ 50,000,000
Maximum period allowed for pending judgment to satisfy or bond (in days)	30				30
Maturities of Long-term Debt [Abstract]
2018	$ 1,125,000				$ 1,125,000
2019	2,250,000				2,250,000
2020	2,250,000				2,250,000
2021	35,513,000				35,513,000
Total senior debt	41,138,000				$ 41,138,000
Minimum [Member]
Senior Debt (Table Details) [Abstract]
Line of credit commitment fee percentage					0.30%
Maximum [Member]
Senior Debt (Table Details) [Abstract]
Line of credit commitment fee percentage					0.50%
Prime Rate [Member]
Senior Debt (Table Details) [Abstract]
Description of variable rate basis					prime
Eurodollar [Member]
Senior Debt (Table Details) [Abstract]
Description of variable rate basis					Eurodollar rate
Term Loan [Member]
Debt Instrument [Line Items]
Senior Debt, Maximum Borrowing Capacity	225,000,000				$ 225,000,000
Senior Debt (Table Details) [Abstract]
Term loan, amount outstanding	41,138,000				$ 41,138,000		48,600,000
Maturity date					Mar. 19, 2021
Term Loan, Periodic Payment, Principal					$ 562,500
Maturities of Long-term Debt [Abstract]
2018	1,125,000				1,125,000
2019	2,250,000				2,250,000
2020	2,250,000				2,250,000
2021	$ 35,513,000				$ 35,513,000
Term Loan [Member] | Prime Rate [Member]
Senior Debt (Table Details) [Abstract]
Margin on Prime Rate, actual	2.00%				2.00%
Term Loan [Member] | Eurodollar [Member]
Senior Debt (Table Details) [Abstract]
Margin on Eurodollar rate, actual	3.00%				3.00%
Revolving Credit Facility [Member]
Senior Debt (Table Details) [Abstract]
Revolving facility, amount outstanding	$ 0				$ 0		85,000,000
Maturity date					Mar. 19, 2019
Senior credit facility, maximum amount	350,000,000				$ 350,000,000
Covenants [Abstract]
Line of Credit Facility, Remaining Borrowing Capacity	245,100,000				245,100,000
Maturities of Long-term Debt [Abstract]
2018	0				0
2019	0				0
2020	0				0
2021	$ 0				$ 0
Revolving Credit Facility [Member] | Prime Rate [Member]
Senior Debt (Table Details) [Abstract]
Margin on Prime Rate, actual	2.00%				2.00%
Revolving Credit Facility [Member] | Prime Rate [Member] | Minimum [Member]
Senior Debt (Table Details) [Abstract]
Basis margin on variable rate					0.50%
Revolving Credit Facility [Member] | Prime Rate [Member] | Maximum [Member]
Senior Debt (Table Details) [Abstract]
Basis margin on variable rate					2.00%
Revolving Credit Facility [Member] | Eurodollar [Member]
Senior Debt (Table Details) [Abstract]
Margin on Eurodollar rate, actual	3.00%				3.00%
Revolving Credit Facility [Member] | Eurodollar [Member] | Minimum [Member]
Senior Debt (Table Details) [Abstract]
Basis margin on variable rate					1.50%
Revolving Credit Facility [Member] | Eurodollar [Member] | Maximum [Member]
Senior Debt (Table Details) [Abstract]
Basis margin on variable rate					3.00%
Line of Credit [Member]
Covenants [Abstract]
Unsecured line of credit, maximum facility	$ 12,500,000				$ 12,500,000
Unsecured line of credit, amount outstanding	0				0		$ 5,700,000
Maturities of Long-term Debt [Abstract]
2018	0				0
2019	0				0
2020	0				0
2021	$ 0				$ 0