Subsidiary Guarantors - Senior Notes Subsidiary Guarantors - Senior Notes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Senior Notes [Line Items]
Carrying value of senior notes	$ 542,740	$ 542,740
Unamortized debt issuance expense	5,200	5,100
Covenant for debt basket available under senior notes	20,000
Event of default for senior notes - failure of other debt payment at maturity in excess of this amount	50,000
Event of default for senior notes - not discharged, bonded or insured judgment in excess of this amount	$ 50,000
Our ownership percentage of subsidiary guarantors of senior notes	100.00%
Senior Notes Due 2020 [Member]
Senior Notes [Line Items]
Initial Borrowing in Senior Notes	$ 300,000
Portion of proceeds from senior notes used to repay outstanding term debt	200,000
Carrying value of senior notes	292,740	292,740
Unamortized debt issuance expense	$ 1,800	2,500
Percentage of original aggreate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Initial Borrowing in Senior Notes	$ 250,000
Portion of proceeds from senior notes used to repay outstanding term debt	200,000
Carrying value of senior notes	250,000	250,000
Unamortized debt issuance expense	$ 2,100	$ 2,800
Percentage of original aggreate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes, Redemption, Period One [Member] | Senior Notes Due 2020 [Member]
Senior Notes [Line Items]
Senior notes, redemption price, percentage	103.313%
Senior Notes, Redemption, Period One [Member] | Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Senior notes, redemption price, percentage	103.563%