Parent Guarantor - Schedule of Condensed Consolidating Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Condensed Financial Statements, Captions [Line Items]
Operating and other revenues	$ 121,282	$ 131,126	$ 330,846	$ 322,334
Operating expenses	(108,686)	(83,172)	(305,276)	(217,042)
General and administrative	(11,048)	(12,696)	(36,109)	(34,427)
Merger transaction expense	(2,078)	(100)	(4,492)	(6,140)
Interest expense	(15,167)	(13,165)	(43,227)	(39,348)
Interest income and other income (expense)	31,141	(51,353)	(54,038)	(126,580)
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	15,444	(29,360)	(112,296)	(101,203)
(Provision for) benefit from income taxes	(4,330)	0	25,271	0
Equity in earnings (loss) of subsidiaries	0	0	0	0
Net Income (Loss)	11,114	(29,360)	(87,025)	(101,203)
Intercompany Eliminations
Condensed Financial Statements, Captions [Line Items]
Operating and other revenues	0	0	0	0
Operating expenses	0	0	0	0
General and administrative	0	0	0	0
Merger transaction expense	0	0	0	0
Interest expense	0	0	0	0
Interest income and other income (expense)	0	0	0	0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0	0	0	0
(Provision for) benefit from income taxes	0	0	0	0
Equity in earnings (loss) of subsidiaries	(11,114)	29,360	87,025	101,203
Net Income (Loss)	(11,114)	29,360	87,025	101,203
Parent Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating and other revenues	0	0	0	0
Operating expenses	0	0	0	0
General and administrative	0	0	0	0
Merger transaction expense	0	0	0	0
Interest expense	0	0	0	0
Interest income and other income (expense)	0	0	0	0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0	0	0	0
(Provision for) benefit from income taxes	0	0	0	0
Equity in earnings (loss) of subsidiaries	11,114	(29,360)	(87,025)	(101,203)
Net Income (Loss)	11,114	(29,360)	(87,025)	(101,203)
Subsidiary Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating and other revenues	121,282	131,126	330,846	322,334
Operating expenses	(108,686)	(83,172)	(305,276)	(217,042)
General and administrative	(11,048)	(12,696)	(36,109)	(34,427)
Merger transaction expense	(2,078)	(100)	(4,492)	(6,140)
Interest expense	(15,167)	(13,165)	(43,227)	(39,348)
Interest income and other income (expense)	31,141	(51,353)	(54,038)	(126,580)
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	15,444	(29,360)	(112,296)	(101,203)
(Provision for) benefit from income taxes	(4,330)	0	25,271	0
Equity in earnings (loss) of subsidiaries	0	0	0	0
Net Income (Loss)	11,114	$ (29,360)	(87,025)	$ (101,203)
Subsidiary Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Operating and other revenues	0		0
Operating expenses	0		0
General and administrative	0		0
Merger transaction expense	0		0
Interest expense	0		0
Interest income and other income (expense)	0		0
Income (loss) before income taxes and equity in earnings (loss) of subsidiaries	0		0
(Provision for) benefit from income taxes	0		0
Equity in earnings (loss) of subsidiaries	0		0
Net Income (Loss)	$ 0		$ 0