Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 09, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt, carrying value	$ 742,094		$ 1,300,000
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt fair value	725,800		1,300,000
Senior notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt fair value	492,200		1,000,000
Debt Instrument, Repurchase Amount		$ 539,000
Mortgage loans | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term debt fair value	$ 233,700		$ 236,200