Guarantor Subsidiaries - Schedule of Condensed Consolidating Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ (29,360)	$ (28,842)	$ (101,203)	$ (60,404)	$ (138,225)
Other comprehensive income (loss)	0	0	0	0
Comprehensive Income (Loss)	(29,360)	(28,842)	(101,203)	(60,404)
Intercompany Eliminations
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	29,360	(12)	101,203	60
Other comprehensive income (loss)	0	0		0
Comprehensive Income (Loss)	29,360	(12)	101,203	60
Parent Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(29,360)		(101,203)
Other comprehensive income (loss)	0		0
Comprehensive Income (Loss)	(29,360)		(101,203)
Parent Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		(28,842)		(60,404)
Other comprehensive income (loss)		0		0
Comprehensive Income (Loss)		(28,842)		(60,404)
Subsidiary Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(29,360)		(101,203)
Other comprehensive income (loss)	0		0
Comprehensive Income (Loss)	$ (29,360)		$ (101,203)
Subsidiary Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net income (loss)		12		(60)
Other comprehensive income (loss)		0		0
Comprehensive Income (Loss)		$ 12		$ (60)