Senior Debt Senior Debt (Details)	3 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Senior Debt [Abstract]
Required minimum consolidated fixed charge coverage ratio		1.10
Actual consolidated fixed charge coverage ratio		0.11
Adjusted consolidated ebitda		$ 5,300,000
Consolidated fixed charges		47,500,000
Debt Instrument [Line Items]
Unamortized debt issuance expense		(5,200,000)	$ (5,100,000)
Mandatory excess cash flow pre-payment		141,000,000	27,000,000
Secured debt, net		134,125,000	186,747,000
Letters of credit, amount outstanding		$ 94,000,000	90,700,000
Commitment fee percentage		0.50%
Equity restrictions		$ 15,000,000
Dividends paid		12,811,000	25,554,000	$ 51,011,000
Senior credit facilities, additional amount allowed		100,000,000
Debt refinancing charges	$ 1,900,000	$ 1,936,000	0	$ 0
Debt arrangement and amendment fees	$ 5,300,000
Event of default - 3rd party ownership % of our voting stock		35.00%
Event of default-not satisfied or bonded judgment in excess of		$ 50,000,000
Maximum period allowed for pending judgment to satisfy		30
Minimum [Member]
Debt Instrument [Line Items]
Commitment fee percentage		0.30%
Maximum [Member]
Debt Instrument [Line Items]
Commitment fee percentage		0.50%
Term Loan [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 225,000,000	225,000,000
Amount outstanding		$ 48,563,000	191,813,000
Maturity date		Mar. 19, 2021
Term loan periodic payment, principal		$ 562,500
Amount available		0	0
Long-term Debt, Fiscal Year Maturity [Abstract]
2018		2,250,000
2019		2,250,000
2020		2,250,000
2021		41,813,000
2022		0
Thereafter		$ 0
Term Loan [Member] | Eurodollar [Member]
Debt Instrument [Line Items]
Margin on variable rate		3.00%
Term Loan [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Margin on variable rate		2.00%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 350,000,000	675,000,000
Amount outstanding		$ 85,000,000	0
Maturity date		Mar. 19, 2019
Amount available		$ 109,700,000	584,304,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2018		0
2019		85,000,000
2020		0
2021		0
2022		0
Thereafter		$ 0
Revolving Credit Facility [Member] | Eurodollar [Member]
Debt Instrument [Line Items]
Margin on variable rate		3.00%
Revolving Credit Facility [Member] | Eurodollar [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis margin on variable rate		1.50%
Revolving Credit Facility [Member] | Eurodollar [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis margin on variable rate		3.00%
Revolving Credit Facility [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Margin on variable rate		2.00%
Revolving Credit Facility [Member] | Prime Rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis margin on variable rate		0.50%
Revolving Credit Facility [Member] | Prime Rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Basis margin on variable rate		2.00%
Term Loan and Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 575,000,000	900,000,000
Amount outstanding		133,563,000	191,813,000
Amount available		109,700,000	584,304,000
Line of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		12,500,000	20,000,000
Amount outstanding		$ 5,735,000	0
Maturity date		Aug. 20, 2018
Amount available		$ 6,765,000	20,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2018		5,735,000
2019		0
2020		0
2021		0
2022		0
Thereafter		0
Senior Debt [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		587,500,000	920,000,000
Amount outstanding		139,298,000	191,813,000
Amount available		116,465,000	$ 604,304,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2018		7,985,000
2019		87,250,000
2020		2,250,000
2021		41,813,000
2022		0
Thereafter		$ 0