Senior Notes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Senior Notes [Line Items]
Carrying value of senior notes	$ 542,740	$ 542,740
Unamortized Debt Issuance Expense	2,100	2,600
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	$ 1,000	1,200
Senior notes, redemption price, percentage	100.00%
Percentage of original aggregate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes Due 2020 [Member] | Senior Notes, Redemption, Period One [Member]
Senior Notes [Line Items]
Senior notes, redemption price, percentage	103.313%
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	$ 1,300	$ 1,500
Senior notes, redemption price, percentage	100.00%
Percentage of original aggregate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes Due 2021 [Member] | Senior Notes, Redemption, Period One [Member]
Senior Notes [Line Items]
Senior notes, redemption price, percentage	103.563%