Fair Value Measurements - Assets Measured at Fair Value on a Non-Recurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill - total reduction in fair value recorded		$ (18,000)	$ (18,026)	$ (18,026)
Property and equipment - total reduction in fair value recorded	$ (34,300)		(34,288)
Non-recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	598		598
Property and equipment	0		0
Level 1 | Non-recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0		0
Property and equipment	0		0
Level 2 | Non-recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0		0
Property and equipment	0		0
Level 3 | Non-recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	598		598
Property and equipment	$ 0		$ 0